From ca907287f224929da842b59604edde29fa0ef189 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Tue, 6 Feb 2024 21:12:53 +0100
Subject: [PATCH 01/13] Explore validation with JSON Schema

---
 lib/jsonapi_plug/document.ex                  |  63 ++++++++---
 lib/jsonapi_plug/document/jsonapi_object.ex   |  22 +++-
 .../document/relationship_object.ex           |  19 ++--
 .../document/resource_identifier_object.ex    |  20 +++-
 lib/jsonapi_plug/document/resource_object.ex  |  58 +++++++---
 lib/jsonapi_plug/exceptions.ex                |  32 ++++--
 lib/jsonapi_plug/normalizer.ex                | 105 ++++++++++++++----
 lib/jsonapi_plug/plug.ex                      |  46 ++++----
 lib/jsonapi_plug/resource.ex                  |  58 +++++++---
 mix.exs                                       |   1 +
 mix.lock                                      |   2 +
 test/jsonapi_plug/plug_test.exs               |   6 +-
 12 files changed, 316 insertions(+), 116 deletions(-)

diff --git a/lib/jsonapi_plug/document.ex b/lib/jsonapi_plug/document.ex
index a7c91f8c..d24d6789 100644
--- a/lib/jsonapi_plug/document.ex
+++ b/lib/jsonapi_plug/document.ex
@@ -8,14 +8,9 @@ defmodule JSONAPIPlug.Document do
   https://jsonapi.org/format/#document-structure
   """
 
-  alias JSONAPIPlug.{
-    Document.ErrorObject,
-    Document.JSONAPIObject,
-    Document.LinkObject,
-    Document.ResourceObject,
-    Exceptions.InvalidDocument,
-    Resource
-  }
+  alias JSONAPIPlug.Document.{ErrorObject, JSONAPIObject, LinkObject, ResourceObject}
+  alias JSONAPIPlug.Exceptions.InvalidDocument
+  alias JSONAPIPlug.Resource
 
   @type value :: String.t() | integer() | float() | [value()] | %{String.t() => value()} | nil
 
@@ -99,7 +94,12 @@ defmodule JSONAPIPlug.Document do
   defp deserialize_data(%{"data" => _data, "errors" => _errors}) do
     raise InvalidDocument,
       message: "Document cannot contain both 'data' and 'errors' members",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document cannot contain both 'data' and 'errors' members",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp deserialize_data(%{"data" => resources}) when is_list(resources),
@@ -124,14 +124,24 @@ defmodule JSONAPIPlug.Document do
        when is_list(included) do
     raise InvalidDocument,
       message: "Document 'included' cannot be present if 'data' isn't also present",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document 'included' cannot be present if 'data' isn't also present",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp deserialize_included(%{"included" => included})
        when not is_nil(included) do
     raise InvalidDocument,
       message: "Document 'included' must be a list",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document 'included' must be a list",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp deserialize_included(_data), do: nil
@@ -152,7 +162,12 @@ defmodule JSONAPIPlug.Document do
   defp deserialize_meta(%{"meta" => meta}) when not is_nil(meta) do
     raise InvalidDocument,
       message: "Document 'meta' must be an object",
-      reference: "https://jsonapi.org/format/#document-meta"
+      errors: [
+        %ErrorObject{
+          title: "Document 'meta' must be an object",
+          detail: "https://jsonapi.org/format/#document-meta"
+        }
+      ]
   end
 
   defp deserialize_meta(_data), do: nil
@@ -183,11 +198,15 @@ defmodule JSONAPIPlug.Document do
 
   defp serialize_data(nil), do: nil
 
-  defp serialize_errors(errors)
-       when not is_nil(errors) and not is_list(errors) do
+  defp serialize_errors(errors) when not is_nil(errors) and not is_list(errors) do
     raise InvalidDocument,
       message: "Document 'errors' must be a list",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document 'errors' must be a list",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp serialize_errors(errors) when is_list(errors),
@@ -199,7 +218,12 @@ defmodule JSONAPIPlug.Document do
        when not is_nil(included) and not is_list(included) do
     raise InvalidDocument,
       message: "Document 'included' must be a list resource objects",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document 'included' must be a list resource objects",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp serialize_included(included) when is_list(included),
@@ -210,7 +234,12 @@ defmodule JSONAPIPlug.Document do
   defp serialize_meta(meta) when not is_nil(meta) and not is_map(meta) do
     raise InvalidDocument,
       message: "Document 'meta' must be a map",
-      reference: "https://jsonapi.org/format/#document-top-level"
+      errors: [
+        %ErrorObject{
+          title: "Document 'meta' must be a map",
+          detail: "https://jsonapi.org/format/#document-top-level"
+        }
+      ]
   end
 
   defp serialize_meta(meta), do: meta
diff --git a/lib/jsonapi_plug/document/jsonapi_object.ex b/lib/jsonapi_plug/document/jsonapi_object.ex
index bb242c2d..03711899 100644
--- a/lib/jsonapi_plug/document/jsonapi_object.ex
+++ b/lib/jsonapi_plug/document/jsonapi_object.ex
@@ -3,7 +3,9 @@ defmodule JSONAPIPlug.Document.JSONAPIObject do
   JSON:API Document JSON:API Object
   """
 
-  alias JSONAPIPlug.{Document, Exceptions.InvalidDocument}
+  alias JSONAPIPlug.Document
+  alias JSONAPIPlug.Document.ErrorObject
+  alias JSONAPIPlug.Exceptions.InvalidDocument
 
   @type version :: :"1.0"
 
@@ -22,8 +24,14 @@ defmodule JSONAPIPlug.Document.JSONAPIObject do
 
   defp deserialize_meta(_jsonapi_object, %{"meta" => _meta}) do
     raise InvalidDocument,
-      message: "JSON:API object 'meta' must be an object",
-      reference: "https://jsonapi.org/format/#document-jsonapi-object"
+      message: "JSON:API Object 'meta' must be an object",
+      errors: [
+        %ErrorObject{
+          title: "JSON:API object 'meta' must be an object",
+          detail: "https://jsonapi.org/format/#document-jsonapi-object",
+          source: %{pointer: "/jsonapi/meta"}
+        }
+      ]
   end
 
   defp deserialize_meta(jsonapi_object, _data), do: jsonapi_object
@@ -37,7 +45,13 @@ defmodule JSONAPIPlug.Document.JSONAPIObject do
   defp deserialize_version(_jsonapi_object, %{"version" => version}) do
     raise InvalidDocument,
       message: "JSON:API Object has invalid version (#{version})",
-      reference: "https://jsonapi.org/format/#document-jsonapi-object"
+      errors: [
+        %ErrorObject{
+          title: "JSON:API Object has invalid version (#{version})",
+          detail: "https://jsonapi.org/format/#document-jsonapi-object",
+          source: %{pointer: "/jsonapi/version"}
+        }
+      ]
   end
 
   defp deserialize_version(jsonapi_object, _data), do: jsonapi_object
diff --git a/lib/jsonapi_plug/document/relationship_object.ex b/lib/jsonapi_plug/document/relationship_object.ex
index 16122792..bd30d54c 100644
--- a/lib/jsonapi_plug/document/relationship_object.ex
+++ b/lib/jsonapi_plug/document/relationship_object.ex
@@ -5,12 +5,9 @@ defmodule JSONAPIPlug.Document.RelationshipObject do
   https://jsonapi.org/format/#document-resource-object-relationships
   """
 
-  alias JSONAPIPlug.{
-    Document,
-    Document.LinkObject,
-    Document.ResourceIdentifierObject,
-    Exceptions.InvalidDocument
-  }
+  alias JSONAPIPlug.Document
+  alias JSONAPIPlug.Document.{ErrorObject, LinkObject, ResourceIdentifierObject}
+  alias JSONAPIPlug.Exceptions.InvalidDocument
 
   @type links :: %{atom() => LinkObject.t()}
 
@@ -62,8 +59,14 @@ defmodule JSONAPIPlug.Document.RelationshipObject do
 
   defp deserialize_meta(_relationship_object, %{"meta" => _meta}) do
     raise InvalidDocument,
-      message: "Relationship object 'meta' must be an object",
-      reference: "https://jsonapi.org/format/#document-resource-object-relationships"
+      message: "Relationship Object 'meta' must be an object",
+      errors: [
+        %ErrorObject{
+          title: "Relationship Object 'meta' must be an object",
+          detail: "https://jsonapi.org/format/#document-resource-object-relationships",
+          source: %{pointer: "/meta"}
+        }
+      ]
   end
 
   defp deserialize_meta(relationship_object, _data), do: relationship_object
diff --git a/lib/jsonapi_plug/document/resource_identifier_object.ex b/lib/jsonapi_plug/document/resource_identifier_object.ex
index 5aeb31de..ee5a68f1 100644
--- a/lib/jsonapi_plug/document/resource_identifier_object.ex
+++ b/lib/jsonapi_plug/document/resource_identifier_object.ex
@@ -5,7 +5,9 @@ defmodule JSONAPIPlug.Document.ResourceIdentifierObject do
   https://jsonapi.org/format/#document-resource-object-linkage
   """
 
-  alias JSONAPIPlug.{Document, Document.ResourceObject, Exceptions.InvalidDocument}
+  alias JSONAPIPlug.Document
+  alias JSONAPIPlug.Document.{ErrorObject, ResourceObject}
+  alias JSONAPIPlug.Exceptions.InvalidDocument
 
   @type t :: %__MODULE__{
           id: ResourceObject.id(),
@@ -28,8 +30,13 @@ defmodule JSONAPIPlug.Document.ResourceIdentifierObject do
 
   defp deserialize_type(_resource_identifier_object, type) do
     raise InvalidDocument,
-      message: "Resource Identifier object type (#{type}) is invalid",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      message: "Resource Identifier object type '#{type}' is invalid",
+      errors: [
+        %ErrorObject{
+          title: "Resource Identifier object type '#{type}' is invalid",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_id(resource_identifier_object, %{"id" => id})
@@ -46,7 +53,12 @@ defmodule JSONAPIPlug.Document.ResourceIdentifierObject do
   defp deserialize_meta(_resource_identifier_object, %{"meta" => _meta}) do
     raise InvalidDocument,
       message: "Resource Identifier object 'meta' must be an object",
-      reference: "https://jsonapi.org/format/#document-resource-identifier-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource Identifier object 'meta' must be an object",
+          detail: "https://jsonapi.org/format/#document-resource-identifier-objects"
+        }
+      ]
   end
 
   defp deserialize_meta(resource_identifier_object, _payload),
diff --git a/lib/jsonapi_plug/document/resource_object.ex b/lib/jsonapi_plug/document/resource_object.ex
index d44626c7..615bf97d 100644
--- a/lib/jsonapi_plug/document/resource_object.ex
+++ b/lib/jsonapi_plug/document/resource_object.ex
@@ -5,12 +5,9 @@ defmodule JSONAPIPlug.Document.ResourceObject do
   https://jsonapi.org/format/#resource_object-resource-objects
   """
 
-  alias JSONAPIPlug.{
-    Document,
-    Document.LinkObject,
-    Document.RelationshipObject,
-    Exceptions.InvalidDocument
-  }
+  alias JSONAPIPlug.Document
+  alias JSONAPIPlug.Document.{ErrorObject, LinkObject, RelationshipObject}
+  alias JSONAPIPlug.Exceptions.InvalidDocument
 
   @type id :: String.t()
   @type type :: String.t()
@@ -63,19 +60,34 @@ defmodule JSONAPIPlug.Document.ResourceObject do
   defp deserialize_type(_resource_object, %{"type" => type}) do
     raise InvalidDocument,
       message: "Resource object type (#{type}) is invalid",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object type (#{type}) is invalid",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_attributes(_resource_object, %{"attributes" => %{"id" => _id}}) do
     raise InvalidDocument,
       message: "Resource object cannot have an attribute named 'id'",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object cannot have an attribute named 'id'",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_attributes(_resource_object, %{"attributes" => %{"type" => _type}}) do
     raise InvalidDocument,
       message: "Resource object cannot have an attribute named 'type'",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object cannot have an attribute named 'type'",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_attributes(resource_object, %{"attributes" => attributes})
@@ -98,13 +110,23 @@ defmodule JSONAPIPlug.Document.ResourceObject do
   defp deserialize_relationships(_resource_object, %{"relationships" => %{"id" => _id}}) do
     raise InvalidDocument,
       message: "Resource object cannot have a relationship named 'id'",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object cannot have a relationship named 'id'",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_relationships(_resource_object, %{"relationships" => %{"type" => _type}}) do
     raise InvalidDocument,
       message: "Resource object cannot have a relationship named 'type'",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object cannot have a relationship named 'type'",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_relationships(
@@ -130,7 +152,12 @@ defmodule JSONAPIPlug.Document.ResourceObject do
        }) do
     raise InvalidDocument,
       message: "Resource object 'relationships' attribute must be an object",
-      reference: "https://jsonapi.org/format/#document-resource-object-relationships"
+      errors: [
+        %ErrorObject{
+          title: "Resource object 'relationships' attribute must be an object",
+          detail: "https://jsonapi.org/format/#document-resource-object-relationships"
+        }
+      ]
   end
 
   defp deserialize_relationships(relationships, _data), do: relationships
@@ -141,7 +168,12 @@ defmodule JSONAPIPlug.Document.ResourceObject do
   defp deserialize_meta(_resource_object, %{"meta" => _meta}) do
     raise InvalidDocument,
       message: "Resource object 'meta' must be an object",
-      reference: "https://jsonapi.org/format/#document-resource-objects"
+      errors: [
+        %ErrorObject{
+          title: "Resource object 'meta' must be an object",
+          detail: "https://jsonapi.org/format/#document-resource-objects"
+        }
+      ]
   end
 
   defp deserialize_meta(resource_object, _data), do: resource_object
diff --git a/lib/jsonapi_plug/exceptions.ex b/lib/jsonapi_plug/exceptions.ex
index 9e5761e5..a5da6081 100644
--- a/lib/jsonapi_plug/exceptions.ex
+++ b/lib/jsonapi_plug/exceptions.ex
@@ -3,22 +3,40 @@ defmodule JSONAPIPlug.Exceptions do
 
   defmodule InvalidDocument do
     @moduledoc """
-    Defines a generic exception for when an invalid document is received.
+    Exception for when an invalid document is received.
     """
-    defexception message: nil, reference: nil
+    alias JSONAPIPlug.Document.ErrorObject
+    defexception message: nil, errors: nil
+
+    @default_error %ErrorObject{
+      status: "500",
+      title: "An error occurred while processing the request.",
+      detail: "Contact the system administrator for assitance."
+    }
 
     @spec exception(keyword()) :: Exception.t()
     def exception(options) do
-      message = Keyword.fetch!(options, :message)
-      reference = Keyword.fetch!(options, :reference)
+      message = List.first(options[:errors], @default_error).title
+
+      %__MODULE__{message: message, errors: options[:errors] || [@default_error]}
+    end
+  end
 
-      %__MODULE__{message: message, reference: reference}
+  defmodule InvalidAttributes do
+    @moduledoc """
+    Exception for when invalid resource attributes are received.
+    """
+    defexception message: nil, errors: nil
+
+    @spec exception(keyword()) :: Exception.t()
+    def exception(options) do
+      %__MODULE__{message: options[:message], errors: options[:errors]}
     end
   end
 
   defmodule InvalidHeader do
     @moduledoc """
-    Defines a generic exception for when an invalid header is received.
+    Exception for when an invalid header is received.
     """
     defexception header: nil, message: nil, reference: nil, status: nil
 
@@ -35,7 +53,7 @@ defmodule JSONAPIPlug.Exceptions do
 
   defmodule InvalidQuery do
     @moduledoc """
-    Defines a generic exception for when an invalid query parameter is received.
+    Exception for when an invalid query parameter is received.
     """
     defexception message: "invalid query",
                  type: nil,
diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index e842923f..661411b2 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -31,17 +31,17 @@ defmodule JSONAPIPlug.Normalizer do
   any point in your normalizer code.
   """
 
-  alias JSONAPIPlug.{
-    API,
-    Document,
-    Document.RelationshipObject,
-    Document.ResourceIdentifierObject,
-    Document.ResourceObject,
-    Exceptions.InvalidDocument,
-    Pagination,
-    Resource
+  alias JSONAPIPlug.{API, Document, Pagination, Resource}
+
+  alias JSONAPIPlug.Document.{
+    ErrorObject,
+    RelationshipObject,
+    ResourceIdentifierObject,
+    ResourceObject
   }
 
+  alias JSONAPIPlug.Exceptions.{InvalidAttributes, InvalidDocument}
+
   alias Plug.Conn
 
   @type t :: module()
@@ -64,7 +64,7 @@ defmodule JSONAPIPlug.Normalizer do
               params() | no_return()
   @callback normalize_attribute(params(), Resource.field_name()) :: value() | no_return()
 
-  @doc "Transforms a JSON:API Document user data"
+  @doc "Transforms a JSON:API Document into user data"
   @spec denormalize(Document.t(), Resource.t(), Conn.t()) :: Conn.params() | no_return()
   def denormalize(%Document{data: nil}, _resource, _conn), do: %{}
 
@@ -103,7 +103,12 @@ defmodule JSONAPIPlug.Normalizer do
     if API.get_config(jsonapi_plug.api, [:client_generated_ids], false) do
       raise InvalidDocument,
         message: "Resource ID not received in request and API requires Client-Generated IDs",
-        reference: "https://jsonapi.org/format/1.0/#crud-creating-client-ids"
+        errors: [
+          %ErrorObject{
+            title: "Resource ID not received in request and API requires Client-Generated IDs",
+            detail: "https://jsonapi.org/format/1.0/#crud-creating-client-ids"
+          }
+        ]
     end
 
     params
@@ -124,6 +129,28 @@ defmodule JSONAPIPlug.Normalizer do
     Enum.reduce(resource.attributes(), params, fn attribute, params ->
       denormalize_attribute(params, resource_object, resource, conn, attribute, case, normalizer)
     end)
+    |> validate_params(resource, case)
+  end
+
+  defp validate_params(params, resource, case) do
+    case resource.validate(params) do
+      :ok ->
+        params
+
+      {:error, errors} ->
+        raise InvalidAttributes,
+          message: "Resource '#{resource.type()}' is invalid.",
+          errors:
+            Enum.map(errors, fn {msg, "#/" <> pointer} ->
+              name = resource.recase_field(pointer, case)
+
+              %ErrorObject{
+                title: "Attribute '#{name}' is invalid.",
+                detail: msg,
+                source: %{pointer: "/data/attributes/" <> name}
+              }
+            end)
+    end
   end
 
   defp denormalize_attribute(params, resource_object, resource, conn, attribute, case, normalizer) do
@@ -184,13 +211,23 @@ defmodule JSONAPIPlug.Normalizer do
 
         {true, _related_data} ->
           raise InvalidDocument,
-            message: "Single resource for many relationship during normalization",
-            reference: nil
+            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            errors: [
+              %ErrorObject{
+                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+                detail: "Relationship '#{name}' is one-to-many but a single value was received."
+              }
+            ]
 
         {false, %RelationshipObject{data: data}} when is_list(data) ->
-          raise InvalidDocument,
-            message: "List of resources for one-to-one relationship during normalization",
-            reference: nil
+        raise InvalidDocument,
+          message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+          errors: [
+            %ErrorObject{
+              title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+              detail: "Relationship '#{name}' is one-to-one but a list was received."
+            }
+          ]
 
         {false, %RelationshipObject{data: nil} = relationship_object} ->
           normalizer.denormalize_relationship(params, relationship_object, key, nil)
@@ -327,13 +364,23 @@ defmodule JSONAPIPlug.Normalizer do
       case {related_many, related_data} do
         {false, related_data} when is_list(related_data) ->
           raise InvalidDocument,
-            message: "List of resources given to render for one-to-one relationship",
-            reference: nil
+            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            errors: [
+              %ErrorObject{
+                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+                detail: "Relationship '#{name}' is one-to-one but a list was received."
+              }
+            ]
 
         {true, _related_data} when not is_list(related_data) ->
           raise InvalidDocument,
-            message: "Single resource given to render for many relationship",
-            reference: nil
+            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            errors: [
+              %ErrorObject{
+                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+                detail: "Relationship '#{name}' is one-to-many but a single value was received."
+              }
+            ]
 
         {_related_many, related_data} ->
           {
@@ -464,13 +511,23 @@ defmodule JSONAPIPlug.Normalizer do
 
       {true, _related_many, related_data} when is_list(related_data) ->
         raise InvalidDocument,
-          message: "List of resources given to render for one-to-one relationship",
-          reference: nil
+          message: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+          errors: [
+            %ErrorObject{
+              title: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+              detail: "Relationship '#{name}' is one-to-one but a list was received."
+            }
+          ]
 
       {true, true, _related_data} ->
         raise InvalidDocument,
-          message: "Single resource given to render for many relationship",
-          reference: nil
+          message: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+          errors: [
+            %ErrorObject{
+              title: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+              detail: "Relationship '#{name}' is one-to-many but a single value was received."
+            }
+          ]
 
       {true, _related_many, related_data} ->
         MapSet.put(
diff --git a/lib/jsonapi_plug/plug.ex b/lib/jsonapi_plug/plug.ex
index e70c233c..d2fac142 100644
--- a/lib/jsonapi_plug/plug.ex
+++ b/lib/jsonapi_plug/plug.ex
@@ -102,9 +102,7 @@ defmodule JSONAPIPlug.Plug do
   require Logger
 
   alias JSONAPIPlug.{Document, Exceptions}
-
   alias JSONAPIPlug.Plug.{ContentTypeNegotiation, Params, QueryParam, ResponseContentType}
-
   alias Plug.Conn
 
   plug :config
@@ -134,33 +132,42 @@ defmodule JSONAPIPlug.Plug do
   end
 
   @impl Plug.ErrorHandler
+  def handle_errors(
+        conn,
+        %{kind: :error, reason: %Exceptions.InvalidAttributes{} = exception, stack: _stack}
+      ) do
+    send_errors(conn, :not_acceptable, exception.errors)
+  end
+
   def handle_errors(
         conn,
         %{kind: :error, reason: %Exceptions.InvalidDocument{} = exception, stack: _stack}
       ) do
-    send_error(conn, :bad_request, %Document.ErrorObject{
-      detail: "#{exception.message}. See #{exception.reference} for more information."
-    })
+    send_errors(conn, :bad_request, exception.errors)
   end
 
   def handle_errors(
         conn,
         %{kind: :error, reason: %Exceptions.InvalidHeader{} = exception, stack: _stack}
       ) do
-    send_error(conn, exception.status, %Document.ErrorObject{
-      detail: "#{exception.message}. See #{exception.reference} for more information.",
-      source: %{pointer: "/header/#{exception.header}"}
-    })
+    send_errors(conn, exception.status, [
+      %Document.ErrorObject{
+        detail: "#{exception.message}. See #{exception.reference} for more information.",
+        source: %{pointer: "/header/#{exception.header}"}
+      }
+    ])
   end
 
   def handle_errors(
         conn,
         %{kind: :error, reason: %Exceptions.InvalidQuery{} = exception, stack: _stack}
       ) do
-    send_error(conn, :bad_request, %Document.ErrorObject{
-      detail: exception.message,
-      source: %{pointer: "/query/#{exception.param}"}
-    })
+    send_errors(conn, :bad_request, [
+      %Document.ErrorObject{
+        detail: exception.message,
+        source: %{pointer: "/query/#{exception.param}"}
+      }
+    ])
   end
 
   def handle_errors(conn, error) do
@@ -168,19 +175,10 @@ defmodule JSONAPIPlug.Plug do
     send_resp(conn, 500, "Something went wrong")
   end
 
-  defp send_error(conn, code, %Document.ErrorObject{} = error) do
-    status_code = Conn.Status.code(code)
-
+  defp send_errors(conn, code, errors) do
     conn
     |> put_resp_content_type(JSONAPIPlug.mime_type())
-    |> send_resp(
-      code,
-      Jason.encode!(%Document{
-        errors: [
-          %{error | status: to_string(status_code), title: Conn.Status.reason_phrase(status_code)}
-        ]
-      })
-    )
+    |> send_resp(code, Jason.encode!(%Document{errors: errors}))
     |> halt()
   end
 end
diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index 9877e593..ff4c16c0 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -90,6 +90,16 @@ defmodule JSONAPIPlug.Resource do
       type: {:or, [:boolean, {:fun, 2}, :mfa]},
       default: true
     ],
+    required: [
+      doc: "Attribute is required.",
+      type: :boolean,
+      default: true
+    ],
+    type: [
+      doc: "Attribute type.",
+      type: {:in, [:string, :number]},
+      default: :string
+    ],
     deserialize: [
       doc:
         "Can be either a boolean, a function reference or MFA returning the attribute value to be deserialized.",
@@ -306,27 +316,55 @@ defmodule JSONAPIPlug.Resource do
          Stream.concat(attributes, relationships)
          |> Enum.find(&(JSONAPIPlug.Resource.field_name(&1) in [:id, :type])) do
       name = JSONAPIPlug.Resource.field_name(field)
-      resource = Module.split(__CALLER__.module) |> List.last()
 
-      raise "Illegal field name '#{name}' for resource #{resource}. See https://jsonapi.org/format/#document-resource-object-fields for more information."
+      raise "Illegal field name '#{name}', see https://jsonapi.org/format/#document-resource-object-fields for more information."
     end
 
     recase_field =
       for field <-
             Stream.concat(attributes, relationships)
-            |> Stream.map(&JSONAPIPlug.Resource.field_name(&1))
+            |> Stream.map(&field_name(&1))
             |> MapSet.new(),
           casing <- [:camelize, :dasherize, :underscore] do
         result = JSONAPIPlug.recase(field, casing)
 
         quote do
-          def recase_field(unquote(field), unquote(casing)) do
-            unquote(result)
-          end
+          def recase_field(unquote(field), unquote(casing)), do: unquote(result)
+          def recase_field(unquote(to_string(field)), unquote(casing)), do: unquote(result)
         end
       end
 
+    schema =
+      %{
+        "type" => "object",
+        "required" =>
+          Enum.reduce(attributes, [], fn attribute, required ->
+            (field_option(attribute, :required) &&
+               [field_name(attribute) |> to_string() | required]) || required
+          end),
+        "properties" =>
+          Enum.reduce(attributes, %{}, fn attribute, properties ->
+            Map.merge(
+              properties,
+              %{
+                (field_name(attribute) |> to_string()) => %{
+                  "type" => (field_option(attribute, :type) || :string) |> to_string()
+                }
+              }
+            )
+          end)
+      }
+      |> ExJsonSchema.Schema.resolve()
+      |> Macro.escape()
+
     quote do
+      # require Exonerate
+
+      def validate(params),
+        do: ExJsonSchema.Validator.validate(unquote(schema), params)
+
+      # Exonerate.function_from_string(:def, :validate, unquote(Jason.encode!(schema)))
+
       @behaviour JSONAPIPlug.Resource
 
       @impl JSONAPIPlug.Resource
@@ -434,13 +472,7 @@ defmodule JSONAPIPlug.Resource do
   @spec for_related_type(t(), ResourceObject.type()) :: t() | nil
   def for_related_type(resource, type) do
     Enum.find_value(resource.relationships(), fn {_relationship, options} ->
-      relationship_resource = Keyword.fetch!(options, :resource)
-
-      if relationship_resource.type() == type do
-        relationship_resource
-      else
-        nil
-      end
+      options[:resource].type() == type && options[:resource]
     end)
   end
 
diff --git a/mix.exs b/mix.exs
index 1184d737..cfbb154a 100644
--- a/mix.exs
+++ b/mix.exs
@@ -40,6 +40,7 @@ defmodule JSONAPIPlug.Mixfile do
       {:credo, "~> 1.0", only: :dev, runtime: false},
       {:dialyxir, "~> 1.0", only: :dev, runtime: false},
       {:ex_doc, "~> 0.20", only: :dev, runtime: false},
+      {:ex_json_schema, "~> 0.10"},
       {:jason, "~> 1.0"},
       {:nimble_options, "~> 0.4 or ~> 0.5 or ~> 1.0"},
       {:plug, "~> 1.0"}
diff --git a/mix.lock b/mix.lock
index 93457e39..19a50428 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,10 +1,12 @@
 %{
   "bunt": {:hex, :bunt, "1.0.0", "081c2c665f086849e6d57900292b3a161727ab40431219529f13c4ddcf3e7a44", [:mix], [], "hexpm", "dc5f86aa08a5f6fa6b8096f0735c4e76d54ae5c9fa2c143e5a1fc7c1cd9bb6b5"},
   "credo": {:hex, :credo, "1.7.6", "b8f14011a5443f2839b04def0b252300842ce7388f3af177157c86da18dfbeea", [:mix], [{:bunt, "~> 0.2.1 or ~> 1.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2 or ~> 1.0", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "146f347fb9f8cbc5f7e39e3f22f70acbef51d441baa6d10169dd604bfbc55296"},
+  "decimal": {:hex, :decimal, "2.1.1", "5611dca5d4b2c3dd497dec8f68751f1f1a54755e8ed2a966c2633cf885973ad6", [:mix], [], "hexpm", "53cfe5f497ed0e7771ae1a475575603d77425099ba5faef9394932b35020ffcc"},
   "dialyxir": {:hex, :dialyxir, "1.4.3", "edd0124f358f0b9e95bfe53a9fcf806d615d8f838e2202a9f430d59566b6b53b", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "bf2cfb75cd5c5006bec30141b131663299c661a864ec7fbbc72dfa557487a986"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.39", "424642f8335b05bb9eb611aa1564c148a8ee35c9c8a8bba6e129d51a3e3c6769", [:mix], [], "hexpm", "06553a88d1f1846da9ef066b87b57c6f605552cfbe40d20bd8d59cc6bde41944"},
   "erlex": {:hex, :erlex, "0.2.6", "c7987d15e899c7a2f34f5420d2a2ea0d659682c06ac607572df55a43753aa12e", [:mix], [], "hexpm", "2ed2e25711feb44d52b17d2780eabf998452f6efda104877a3881c2f8c0c0c75"},
   "ex_doc": {:hex, :ex_doc, "0.34.0", "ab95e0775db3df71d30cf8d78728dd9261c355c81382bcd4cefdc74610bef13e", [:mix], [{:earmark_parser, "~> 1.4.39", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.0", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14 or ~> 1.0", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1 or ~> 1.0", [hex: :makeup_erlang, repo: "hexpm", optional: false]}, {:makeup_html, ">= 0.1.0", [hex: :makeup_html, repo: "hexpm", optional: true]}], "hexpm", "60734fb4c1353f270c3286df4a0d51e65a2c1d9fba66af3940847cc65a8066d7"},
+  "ex_json_schema": {:hex, :ex_json_schema, "0.10.2", "7c4b8c1481fdeb1741e2ce66223976edfb9bccebc8014f6aec35d4efe964fb71", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}], "hexpm", "37f43be60f8407659d4d0155a7e45e7f406dab1f827051d3d35858a709baf6a6"},
   "file_system": {:hex, :file_system, "1.0.0", "b689cc7dcee665f774de94b5a832e578bd7963c8e637ef940cd44327db7de2cd", [:mix], [], "hexpm", "6752092d66aec5a10e662aefeed8ddb9531d79db0bc145bb8c40325ca1d8536d"},
   "jason": {:hex, :jason, "1.4.1", "af1504e35f629ddcdd6addb3513c3853991f694921b1b9368b0bd32beb9f1b63", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "fbb01ecdfd565b56261302f7e1fcc27c4fb8f32d56eab74db621fc154604a7a1"},
   "makeup": {:hex, :makeup, "1.1.2", "9ba8837913bdf757787e71c1581c21f9d2455f4dd04cfca785c70bbfff1a76a3", [:mix], [{:nimble_parsec, "~> 1.2.2 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "cce1566b81fbcbd21eca8ffe808f33b221f9eee2cbc7a1706fc3da9ff18e6cac"},
diff --git a/test/jsonapi_plug/plug_test.exs b/test/jsonapi_plug/plug_test.exs
index 5b3155a9..54777f35 100644
--- a/test/jsonapi_plug/plug_test.exs
+++ b/test/jsonapi_plug/plug_test.exs
@@ -186,7 +186,8 @@ defmodule JSONAPIPlug.PlugTest do
                      "id" => "1",
                      "type" => "user",
                      "attributes" => %{
-                       "firstName" => "Jerome"
+                       "firstName" => "Jerome",
+                       "lastName" => "finch"
                      },
                      "relationships" => %{
                        "company" => %{
@@ -229,7 +230,8 @@ defmodule JSONAPIPlug.PlugTest do
                      "id" => "1",
                      "type" => "user",
                      "attributes" => %{
-                       "firstName" => "Jerome"
+                       "firstName" => "Jerome",
+                       "lastName" => "Finch"
                      }
                    },
                    "included" => [

From ccef5c965510fd270b6b471b10b3bc171eee28f6 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Tue, 6 Feb 2024 21:16:22 +0100
Subject: [PATCH 02/13] Update lib/jsonapi_plug/resource.ex

---
 lib/jsonapi_plug/resource.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index ff4c16c0..9cf59064 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -472,7 +472,7 @@ defmodule JSONAPIPlug.Resource do
   @spec for_related_type(t(), ResourceObject.type()) :: t() | nil
   def for_related_type(resource, type) do
     Enum.find_value(resource.relationships(), fn {_relationship, options} ->
-      options[:resource].type() == type && options[:resource]
+      if options[:resource].type() == type, do: options[:resource]
     end)
   end
 

From 456ef7e33ea8af042f1b611abcdf35fa023ce00a Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Tue, 6 Feb 2024 21:23:33 +0100
Subject: [PATCH 03/13] Cleanup

---
 lib/jsonapi_plug/resource.ex | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index 9cf59064..9f930a59 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -358,13 +358,6 @@ defmodule JSONAPIPlug.Resource do
       |> Macro.escape()
 
     quote do
-      # require Exonerate
-
-      def validate(params),
-        do: ExJsonSchema.Validator.validate(unquote(schema), params)
-
-      # Exonerate.function_from_string(:def, :validate, unquote(Jason.encode!(schema)))
-
       @behaviour JSONAPIPlug.Resource
 
       @impl JSONAPIPlug.Resource
@@ -431,6 +424,10 @@ defmodule JSONAPIPlug.Resource do
           raise "invalid action #{action}, use one of create.json, index.json, show.json, update.json"
         end
       end
+
+      @doc false
+      def validate(params),
+        do: ExJsonSchema.Validator.validate(unquote(schema), params)
     end
   end
 

From ce00f4c4106d3fc9ff699e6eebf558b6906c8bf6 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Sat, 25 May 2024 14:23:23 +0200
Subject: [PATCH 04/13] Format

---
 lib/jsonapi_plug/normalizer.ex | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index 661411b2..41089b36 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -220,14 +220,14 @@ defmodule JSONAPIPlug.Normalizer do
             ]
 
         {false, %RelationshipObject{data: data}} when is_list(data) ->
-        raise InvalidDocument,
-          message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
-          errors: [
-            %ErrorObject{
-              title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
-              detail: "Relationship '#{name}' is one-to-one but a list was received."
-            }
-          ]
+          raise InvalidDocument,
+            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            errors: [
+              %ErrorObject{
+                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+                detail: "Relationship '#{name}' is one-to-one but a list was received."
+              }
+            ]
 
         {false, %RelationshipObject{data: nil} = relationship_object} ->
           normalizer.denormalize_relationship(params, relationship_object, key, nil)

From 5b49569883057f95bec7733e24f6853001d84d3b Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Tue, 6 Feb 2024 21:12:53 +0100
Subject: [PATCH 05/13] Explore validation with JSON Schema

---
 lib/jsonapi_plug/resource.ex | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index 9f930a59..0a3ed187 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -358,6 +358,13 @@ defmodule JSONAPIPlug.Resource do
       |> Macro.escape()
 
     quote do
+      # require Exonerate
+
+      def validate(params),
+        do: ExJsonSchema.Validator.validate(unquote(schema), params)
+
+      # Exonerate.function_from_string(:def, :validate, unquote(Jason.encode!(schema)))
+
       @behaviour JSONAPIPlug.Resource
 
       @impl JSONAPIPlug.Resource

From 4f9dd26603f987b61d347b2c12a92f323b97ad6a Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Thu, 6 Jun 2024 21:03:26 +0200
Subject: [PATCH 06/13] Remove duplicate dunction

---
 lib/jsonapi_plug/resource.ex | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index 0a3ed187..9cf59064 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -431,10 +431,6 @@ defmodule JSONAPIPlug.Resource do
           raise "invalid action #{action}, use one of create.json, index.json, show.json, update.json"
         end
       end
-
-      @doc false
-      def validate(params),
-        do: ExJsonSchema.Validator.validate(unquote(schema), params)
     end
   end
 

From c85bd22472bc23763fdfa09135027e0096fde276 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Wed, 2 Oct 2024 00:41:14 +0200
Subject: [PATCH 07/13] Adapt to protocols

---
 lib/jsonapi_plug.ex                          | 18 +++--
 lib/jsonapi_plug/document/resource_object.ex |  4 +-
 lib/jsonapi_plug/normalizer.ex               | 68 ++++++++++-------
 lib/jsonapi_plug/resource.ex                 | 79 +++++++++-----------
 mix.lock                                     |  1 +
 test/jsonapi_plug/plug_test.exs              |  2 +-
 test/support/resources.ex                    |  2 +-
 7 files changed, 95 insertions(+), 79 deletions(-)

diff --git a/lib/jsonapi_plug.ex b/lib/jsonapi_plug.ex
index 894fb47d..2af8099b 100644
--- a/lib/jsonapi_plug.ex
+++ b/lib/jsonapi_plug.ex
@@ -200,6 +200,16 @@ defmodule JSONAPIPlug do
       doc: "Controls wether the attribute is deserialized in requests.",
       type: :boolean,
       default: true
+    ],
+    required: [
+      doc: "Attribute is required.",
+      type: :boolean,
+      default: false
+    ],
+    type: [
+      doc: "Attribute type",
+      type: {:in, [:string, :number]},
+      default: :string
     ]
   ]
 
@@ -225,12 +235,8 @@ defmodule JSONAPIPlug do
               doc:
                 "Resource attributes. This will be used to (de)serialize requests/responses:\n\n" <>
                   NimbleOptions.docs(@attribute_schema, nest_level: 1),
-              type:
-                {:or,
-                 [
-                   {:list, :atom},
-                   {:keyword_list, [*: [type: [keyword_list: [keys: @attribute_schema]]]]}
-                 ]},
+              type: :keyword_list,
+              keys: [*: [type: :keyword_list, keys: @attribute_schema]],
               default: []
             ],
             id_attribute: [
diff --git a/lib/jsonapi_plug/document/resource_object.ex b/lib/jsonapi_plug/document/resource_object.ex
index 931c9cd8..dffb15fc 100644
--- a/lib/jsonapi_plug/document/resource_object.ex
+++ b/lib/jsonapi_plug/document/resource_object.ex
@@ -11,12 +11,13 @@ defmodule JSONAPIPlug.Document.ResourceObject do
 
   @type id :: String.t()
   @type type :: String.t()
+  @type attributes :: %{String.t() => Document.value()}
 
   @type t :: %__MODULE__{
           id: id(),
           lid: id(),
           type: type(),
-          attributes: %{String.t() => Document.value()} | nil,
+          attributes: attributes() | nil,
           links: Document.links() | nil,
           meta: Document.meta() | nil,
           relationships: %{String.t() => [RelationshipObject.t()]} | nil
@@ -65,6 +66,7 @@ defmodule JSONAPIPlug.Document.ResourceObject do
           title: "Resource object type (#{type}) is invalid",
           detail: "https://jsonapi.org/format/#document-resource-objects"
         }
+      ]
   end
 
   defp deserialize_attributes(_resource_object, %{"attributes" => %{"id" => _id}}) do
diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index 8a53b920..bcbdcaa0 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -31,8 +31,12 @@ defmodule JSONAPIPlug.Normalizer do
   any point in your normalizer code.
   """
 
+  alias JSONAPIPlug.Resource.ErrorFormatter
+
   alias JSONAPIPlug.{
     Document,
+    Document,
+    Document.ErrorObject,
     Document.RelationshipObject,
     Document.ResourceIdentifierObject,
     Document.ResourceObject,
@@ -146,29 +150,31 @@ defmodule JSONAPIPlug.Normalizer do
     end
   end
 
-  defp denormalize_attributes(params, %ResourceObject{} = resource_object, resource, conn) do
-    Enum.reduce(Resource.attributes(resource), params, &denormalize_attribute(&2, resource_object, resource, &1, conn))
-    |> validate_params(resource, case)
+  defp denormalize_attributes(
+         params,
+         %ResourceObject{} = resource_object,
+         resource,
+         conn
+       ) do
+    Enum.reduce(
+      Resource.attributes(resource),
+      params,
+      &denormalize_attribute(&2, resource_object, resource, &1, conn)
+    )
+    |> validate_params(resource, conn)
   end
 
-  defp validate_params(params, resource, case) do
-    case resource.validate(params) do
+  defp validate_params(params, resource, %Conn{
+         private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
+       }) do
+    case Resource.validate(resource, params) do
       :ok ->
         params
 
       {:error, errors} ->
         raise InvalidAttributes,
-          message: "Resource '#{resource.type()}' is invalid.",
-          errors:
-            Enum.map(errors, fn {msg, "#/" <> pointer} ->
-              name = resource.recase_field(pointer, case)
-
-              %ErrorObject{
-                title: "Attribute '#{name}' is invalid.",
-                detail: msg,
-                source: %{pointer: "/data/attributes/" <> name}
-              }
-            end)
+          message: "Resource '#{Resource.type(resource)}' is invalid.",
+          errors: ErrorFormatter.format(errors, resource, jsonapi_plug.config[:case])
     end
   end
 
@@ -404,21 +410,21 @@ defmodule JSONAPIPlug.Normalizer do
       case {related_many, related_resource} do
         {false, related_resources} when is_list(related_resources) ->
           raise InvalidDocument,
-            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            message: "Invalid value for '#{Resource.type(resource)}' relationship '#{key}'",
             errors: [
               %ErrorObject{
-                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
-                detail: "Relationship '#{name}' is one-to-one but a list was received."
+                title: "Invalid value for '#{Resource.type(resource)}' relationship '#{key}'",
+                detail: "Relationship '#{key}' is one-to-one but a list was received."
               }
             ]
 
         {true, _related_resource} when not is_list(related_resource) ->
           raise InvalidDocument,
-            message: "Invalid value for '#{resource.type()}' relationship '#{name}'",
+            message: "Invalid value for '#{Resource.type(resource)}' relationship '#{key}'",
             errors: [
               %ErrorObject{
-                title: "Invalid value for '#{resource.type()}' relationship '#{name}'",
-                detail: "Relationship '#{name}' is one-to-many but a single value was received."
+                title: "Invalid value for '#{Resource.type(resource)}' relationship '#{key}'",
+                detail: "Relationship '#{key}' is one-to-many but a single value was received."
               }
             ]
 
@@ -513,6 +519,7 @@ defmodule JSONAPIPlug.Normalizer do
     related_data = Map.get(resource, relationship)
     related_loaded? = relationship_loaded?(related_data)
     related_many = Resource.field_option(resource, relationship, :many)
+    related_resource = struct(Resource.field_option(resource, relationship, :resource))
 
     case {related_loaded?, related_many, related_data} do
       {true, true, related_data} when is_list(related_data) ->
@@ -523,21 +530,26 @@ defmodule JSONAPIPlug.Normalizer do
 
       {true, _related_many, related_data} when is_list(related_data) ->
         raise InvalidDocument,
-          message: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+          message:
+            "Invalid value for '#{Resource.type(related_resource)}' relationship '#{relationship}'",
           errors: [
             %ErrorObject{
-              title: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
-              detail: "Relationship '#{name}' is one-to-one but a list was received."
+              title:
+                "Invalid value for '#{Resource.type(related_resource)}' relationship '#{relationship}'",
+              detail: "Relationship '#{relationship}' is one-to-one but a list was received."
             }
           ]
 
       {true, true, _related_data} ->
         raise InvalidDocument,
-          message: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
+          message:
+            "Invalid value for '#{Resource.type(related_resource)}' relationship '#{relationship}'",
           errors: [
             %ErrorObject{
-              title: "Invalid value for '#{related_resource.type()}' relationship '#{name}'",
-              detail: "Relationship '#{name}' is one-to-many but a single value was received."
+              title:
+                "Invalid value for '#{Resource.type(related_resource)}' relationship '#{relationship}'",
+              detail:
+                "Relationship '#{relationship}' is one-to-many but a single value was received."
             }
           ]
 
diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index a6ef7098..9dfb1a27 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -148,11 +148,12 @@ defprotocol JSONAPIPlug.Resource do
   """
   @spec type(t()) :: ResourceObject.type()
   def type(resource)
-  
+
   @doc """
   Validates the resource
   """
-  def validate(resource)
+  @spec validate(t(), ResourceObject.attributes()) :: :ok | {:error, term()}
+  def validate(resource, attributes)
 end
 
 defimpl JSONAPIPlug.Resource, for: Any do
@@ -160,7 +161,14 @@ defimpl JSONAPIPlug.Resource, for: Any do
     options =
       options
       |> Macro.prewalk(&Macro.expand(&1, __CALLER__))
-      |> NimbleOptions.validate!(JSONAPIPlug.resource_options_schema())      
+      |> Keyword.update(:attributes, [], fn attributes ->
+        Enum.map(attributes, fn
+          {field_name, nil} -> {field_name, []}
+          {field_name, field_options} -> {field_name, field_options}
+          field_name -> {field_name, []}
+        end)
+      end)
+      |> NimbleOptions.validate!(JSONAPIPlug.resource_options_schema())
 
     attributes = generate_attributes(options)
     relationships = generate_relationships(options)
@@ -168,7 +176,7 @@ defimpl JSONAPIPlug.Resource, for: Any do
     check_fields(attributes, relationships, options)
 
     field_option = generate_field_option(options)
-    recase_field = generate_recase_field(options)
+    recase_field = generate_recase_field(attributes, relationships)
     schema = generate_schema(options)
 
     quote do
@@ -189,25 +197,20 @@ defimpl JSONAPIPlug.Resource, for: Any do
         unquote(recase_field)
         def relationships(_resource), do: unquote(relationships)
         def type(_resource), do: unquote(options[:type])
-        def validate(params),
-         do: ExJsonSchema.Validator.validate(unquote(schema), params)
+
+        def validate(_resource, params) do
+          ExJsonSchema.Validator.validate(unquote(schema), params, error_formatter: false)
+        end
       end
     end
   end
 
-
   defp generate_attributes(options) do
-    Enum.map(options[:attributes] || [], fn
-      {field_name, _field_options} -> field_name
-      field_name -> field_name
-    end)
+    Enum.map(options[:attributes] || [], fn {attribute, _options} -> attribute end)
   end
 
   defp generate_relationships(options) do
-    Enum.map(options[:relationships] || [], fn
-      {field_name, _field_options} -> field_name
-      field_name -> field_name
-    end)
+    Enum.map(options[:relationships] || [], fn {relationship, _options} -> relationship end)
   end
 
   defp check_fields(attributes, relationships, options) do
@@ -226,11 +229,6 @@ defimpl JSONAPIPlug.Resource, for: Any do
 
   defp generate_field_option(options) do
     Stream.concat(options[:attributes], options[:relationships])
-    |> Stream.map(fn
-      {field_name, nil} -> {field_name, []}
-      {field_name, field_options} -> {field_name, field_options}
-      field_name -> {field_name, []}
-    end)
     |> Enum.flat_map(fn {field_name, field_options} ->
       Enum.map(field_options, fn {field_option, value} ->
         quote do
@@ -241,40 +239,36 @@ defimpl JSONAPIPlug.Resource, for: Any do
     end)
   end
 
-  defp generate_recase_field(options) do
-    Stream.concat(options[:attributes], options[:relationships])
-    |> Stream.map(fn
-      {field_name, _field_options} -> field_name
-      field_name -> field_name
-    end)
+  defp generate_recase_field(attributes, relationships) do
+    Stream.concat(attributes, relationships)
     |> Enum.flat_map(fn field_name ->
       Enum.map([:camelize, :dasherize, :underscore], fn field_case ->
+        recased = JSONAPIPlug.recase(field_name, field_case)
+
         quote do
           def recase_field(_resource, unquote(field_name), unquote(field_case)),
-            do: unquote(JSONAPIPlug.recase(field_name, field_case))
+            do: unquote(recased)
+
+          def recase_field(_resource, unquote(to_string(field_name)), unquote(field_case)),
+            do: unquote(recased)
         end
       end)
     end)
   end
-  
-  def generate_schema do
-      %{
+
+  def generate_schema(options) do
+    %{
       "type" => "object",
       "required" =>
-        Enum.reduce(attributes, [], fn attribute, required ->
-          (field_option(attribute, :required) &&
-             [field_name(attribute) |> to_string() | required]) || required
+        Enum.reduce(options[:attributes], [], fn {attribute, options}, required ->
+          (options[:required] && [to_string(options[:name] || attribute) | required]) || required
         end),
       "properties" =>
-        Enum.reduce(attributes, %{}, fn attribute, properties ->
-          Map.merge(
-            properties,
-            %{
-              (field_name(attribute) |> to_string()) => %{
-                "type" => (field_option(attribute, :type) || :string) |> to_string()
-              }
-            }
-          )
+        Enum.into(options[:attributes], %{}, fn {attribute, options} ->
+          {
+            to_string(options[:name] || attribute),
+            %{"type" => to_string(options[:type] || :string)}
+          }
         end)
     }
     |> ExJsonSchema.Schema.resolve()
@@ -289,4 +283,5 @@ defimpl JSONAPIPlug.Resource, for: Any do
   def recase_field(_resource, field, _case), do: field
   def relationships(_resource), do: []
   def type(_resource), do: ""
+  def validate(_resource, _params), do: :ok
 end
diff --git a/mix.lock b/mix.lock
index 3f1be227..11f9c6c1 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,6 +1,7 @@
 %{
   "bunt": {:hex, :bunt, "1.0.0", "081c2c665f086849e6d57900292b3a161727ab40431219529f13c4ddcf3e7a44", [:mix], [], "hexpm", "dc5f86aa08a5f6fa6b8096f0735c4e76d54ae5c9fa2c143e5a1fc7c1cd9bb6b5"},
   "credo": {:hex, :credo, "1.7.8", "9722ba1681e973025908d542ec3d95db5f9c549251ba5b028e251ad8c24ab8c5", [:mix], [{:bunt, "~> 0.2.1 or ~> 1.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2 or ~> 1.0", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "cb9e87cc64f152f3ed1c6e325e7b894dea8f5ef2e41123bd864e3cd5ceb44968"},
+  "decimal": {:hex, :decimal, "2.1.1", "5611dca5d4b2c3dd497dec8f68751f1f1a54755e8ed2a966c2633cf885973ad6", [:mix], [], "hexpm", "53cfe5f497ed0e7771ae1a475575603d77425099ba5faef9394932b35020ffcc"},
   "dialyxir": {:hex, :dialyxir, "1.4.4", "fb3ce8741edeaea59c9ae84d5cec75da00fa89fe401c72d6e047d11a61f65f70", [:mix], [{:erlex, ">= 0.2.7", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "cd6111e8017ccd563e65621a4d9a4a1c5cd333df30cebc7face8029cacb4eff6"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.41", "ab34711c9dc6212dda44fcd20ecb87ac3f3fce6f0ca2f28d4a00e4154f8cd599", [:mix], [], "hexpm", "a81a04c7e34b6617c2792e291b5a2e57ab316365c2644ddc553bb9ed863ebefa"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},
diff --git a/test/jsonapi_plug/plug_test.exs b/test/jsonapi_plug/plug_test.exs
index c5cdad9a..eda1a38d 100644
--- a/test/jsonapi_plug/plug_test.exs
+++ b/test/jsonapi_plug/plug_test.exs
@@ -137,7 +137,7 @@ defmodule JSONAPIPlug.PlugTest do
                      "type" => "user",
                      "attributes" => %{
                        "firstName" => "Jerome",
-                       "lastName" => "finch"
+                       "lastName" => "Finch"
                      },
                      "relationships" => %{
                        "company" => %{
diff --git a/test/support/resources.ex b/test/support/resources.ex
index aebd5cba..70eeec83 100644
--- a/test/support/resources.ex
+++ b/test/support/resources.ex
@@ -40,7 +40,7 @@ defmodule JSONAPIPlug.TestSupport.Resources do
       JSONAPIPlug.Resource,
       type: "user",
       attributes: [
-        age: nil,
+        age: [type: :number],
         first_name: nil,
         last_name: nil,
         full_name: [deserialize: false],

From 6ac5c066b997e98339e66c0984eb18fbcce3c91c Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Thu, 6 Jun 2024 21:17:15 +0200
Subject: [PATCH 08/13] Move function definition

---
 lib/jsonapi_plug/resource/error_formatter.ex | 25 ++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 lib/jsonapi_plug/resource/error_formatter.ex

diff --git a/lib/jsonapi_plug/resource/error_formatter.ex b/lib/jsonapi_plug/resource/error_formatter.ex
new file mode 100644
index 00000000..f3b0176b
--- /dev/null
+++ b/lib/jsonapi_plug/resource/error_formatter.ex
@@ -0,0 +1,25 @@
+defmodule JSONAPIPlug.Resource.ErrorFormatter do
+  @moduledoc false
+
+  alias ExJsonSchema.Validator.Error
+  alias JSONAPIPlug.Document.ErrorObject
+  alias JSONAPIPlug.Resource
+
+  def format(errors, resource, case) do
+    Enum.flat_map(errors, fn %Error{error: error, path: "#" <> path} ->
+      format_error(error, resource, case, "/data/attributes/" <> path)
+    end)
+  end
+
+  defp format_error(%Error.Required{} = error, resource, case, base_path) do
+    Enum.map(error.missing, fn attribute ->
+      %ErrorObject{
+        title: "Campo obbligatorio",
+        detail: "Questo campo è obbligatorio.",
+        status: 422,
+        code: :unprocessable_entity,
+        source: %{pointer: base_path <> Resource.recase_field(resource, attribute, case)}
+      }
+    end)
+  end
+end

From bc6d6bb5f22ba1123eca07cabc7b7ef4448ee24b Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Wed, 2 Oct 2024 21:06:08 +0200
Subject: [PATCH 09/13] Don't validate params on patch

---
 lib/jsonapi_plug/normalizer.ex | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index bcbdcaa0..675c61e7 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -161,12 +161,12 @@ defmodule JSONAPIPlug.Normalizer do
       params,
       &denormalize_attribute(&2, resource_object, resource, &1, conn)
     )
-    |> validate_params(resource, conn)
+    |> validate_attributes(resource, conn)
   end
 
-  defp validate_params(params, resource, %Conn{
-         private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
-       }) do
+  defp validate_attributes(params, _resource, %Conn{method: "PATCH"}), do: params
+
+  defp validate_attributes(params, resource, %Conn{private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}}) do
     case Resource.validate(resource, params) do
       :ok ->
         params

From 52180034f9399244d088034771beb82794a7a065 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Wed, 2 Oct 2024 21:07:58 +0200
Subject: [PATCH 10/13] Format

---
 lib/jsonapi_plug/normalizer.ex | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index 675c61e7..9e3d499a 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -166,7 +166,9 @@ defmodule JSONAPIPlug.Normalizer do
 
   defp validate_attributes(params, _resource, %Conn{method: "PATCH"}), do: params
 
-  defp validate_attributes(params, resource, %Conn{private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}}) do
+  defp validate_attributes(params, resource, %Conn{
+         private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
+       }) do
     case Resource.validate(resource, params) do
       :ok ->
         params

From 93a4d21e6c54c695041e623a2867bd994e48db8b Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Thu, 3 Oct 2024 00:57:25 +0200
Subject: [PATCH 11/13] Split validation to protocol

---
 lib/jsonapi_plug/normalizer.ex               | 48 +++++++-------------
 lib/jsonapi_plug/resource.ex                 | 21 ++++-----
 lib/jsonapi_plug/resource/error_formatter.ex | 25 ----------
 3 files changed, 27 insertions(+), 67 deletions(-)
 delete mode 100644 lib/jsonapi_plug/resource/error_formatter.ex

diff --git a/lib/jsonapi_plug/normalizer.ex b/lib/jsonapi_plug/normalizer.ex
index 9e3d499a..44fc9f1d 100644
--- a/lib/jsonapi_plug/normalizer.ex
+++ b/lib/jsonapi_plug/normalizer.ex
@@ -31,24 +31,16 @@ defmodule JSONAPIPlug.Normalizer do
   any point in your normalizer code.
   """
 
-  alias JSONAPIPlug.Resource.ErrorFormatter
-
-  alias JSONAPIPlug.{
-    Document,
-    Document,
-    Document.ErrorObject,
-    Document.RelationshipObject,
-    Document.ResourceIdentifierObject,
-    Document.ResourceObject,
-    Exceptions.InvalidDocument,
-    Pagination,
-    Resource,
-    Resource.Attribute,
-    Resource.Links,
-    Resource.Meta
-  }
-
+  alias JSONAPIPlug.{Document, Pagination, Resource}
   alias JSONAPIPlug.Exceptions.{InvalidAttributes, InvalidDocument}
+  alias JSONAPIPlug.Resource.{Attribute, Links, Meta, Validator}
+
+  alias JSONAPIPlug.Document.{
+    ErrorObject,
+    RelationshipObject,
+    ResourceIdentifierObject,
+    ResourceObject
+  }
 
   alias Plug.Conn
 
@@ -156,27 +148,21 @@ defmodule JSONAPIPlug.Normalizer do
          resource,
          conn
        ) do
-    Enum.reduce(
-      Resource.attributes(resource),
-      params,
-      &denormalize_attribute(&2, resource_object, resource, &1, conn)
-    )
-    |> validate_attributes(resource, conn)
-  end
-
-  defp validate_attributes(params, _resource, %Conn{method: "PATCH"}), do: params
+    params =
+      Enum.reduce(
+        Resource.attributes(resource),
+        params,
+        &denormalize_attribute(&2, resource_object, resource, &1, conn)
+      )
 
-  defp validate_attributes(params, resource, %Conn{
-         private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
-       }) do
-    case Resource.validate(resource, params) do
+    case Validator.validate(resource, params, conn) do
       :ok ->
         params
 
       {:error, errors} ->
         raise InvalidAttributes,
           message: "Resource '#{Resource.type(resource)}' is invalid.",
-          errors: ErrorFormatter.format(errors, resource, jsonapi_plug.config[:case])
+          errors: errors
     end
   end
 
diff --git a/lib/jsonapi_plug/resource.ex b/lib/jsonapi_plug/resource.ex
index 9dfb1a27..5e14cae9 100644
--- a/lib/jsonapi_plug/resource.ex
+++ b/lib/jsonapi_plug/resource.ex
@@ -141,6 +141,14 @@ defprotocol JSONAPIPlug.Resource do
   @spec relationships(t()) :: [field_name()]
   def relationships(resource)
 
+  @doc """
+  Resource schema
+
+  Returns an ExJsonSchema used to validate resource attributes.
+  """
+  @spec schema(t()) :: term()
+  def schema(resource)
+
   @doc """
   Resource Type
 
@@ -148,12 +156,6 @@ defprotocol JSONAPIPlug.Resource do
   """
   @spec type(t()) :: ResourceObject.type()
   def type(resource)
-
-  @doc """
-  Validates the resource
-  """
-  @spec validate(t(), ResourceObject.attributes()) :: :ok | {:error, term()}
-  def validate(resource, attributes)
 end
 
 defimpl JSONAPIPlug.Resource, for: Any do
@@ -196,11 +198,8 @@ defimpl JSONAPIPlug.Resource, for: Any do
         def path(_resource), do: unquote(options[:path])
         unquote(recase_field)
         def relationships(_resource), do: unquote(relationships)
+        def schema(_resource), do: unquote(schema)
         def type(_resource), do: unquote(options[:type])
-
-        def validate(_resource, params) do
-          ExJsonSchema.Validator.validate(unquote(schema), params, error_formatter: false)
-        end
       end
     end
   end
@@ -282,6 +281,6 @@ defimpl JSONAPIPlug.Resource, for: Any do
   def path(_resource), do: nil
   def recase_field(_resource, field, _case), do: field
   def relationships(_resource), do: []
+  def schema(_resource), do: nil
   def type(_resource), do: ""
-  def validate(_resource, _params), do: :ok
 end
diff --git a/lib/jsonapi_plug/resource/error_formatter.ex b/lib/jsonapi_plug/resource/error_formatter.ex
deleted file mode 100644
index f3b0176b..00000000
--- a/lib/jsonapi_plug/resource/error_formatter.ex
+++ /dev/null
@@ -1,25 +0,0 @@
-defmodule JSONAPIPlug.Resource.ErrorFormatter do
-  @moduledoc false
-
-  alias ExJsonSchema.Validator.Error
-  alias JSONAPIPlug.Document.ErrorObject
-  alias JSONAPIPlug.Resource
-
-  def format(errors, resource, case) do
-    Enum.flat_map(errors, fn %Error{error: error, path: "#" <> path} ->
-      format_error(error, resource, case, "/data/attributes/" <> path)
-    end)
-  end
-
-  defp format_error(%Error.Required{} = error, resource, case, base_path) do
-    Enum.map(error.missing, fn attribute ->
-      %ErrorObject{
-        title: "Campo obbligatorio",
-        detail: "Questo campo è obbligatorio.",
-        status: 422,
-        code: :unprocessable_entity,
-        source: %{pointer: base_path <> Resource.recase_field(resource, attribute, case)}
-      }
-    end)
-  end
-end

From 65531ae811dcffe360ba103aabaf5dcf4fd213a4 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Thu, 3 Oct 2024 00:57:36 +0200
Subject: [PATCH 12/13] Split validation to protocol

---
 lib/jsonapi_plug/resource/validator.ex        | 52 +++++++++++++++++++
 .../resource/validator/error_formatter.ex     | 25 +++++++++
 2 files changed, 77 insertions(+)
 create mode 100644 lib/jsonapi_plug/resource/validator.ex
 create mode 100644 lib/jsonapi_plug/resource/validator/error_formatter.ex

diff --git a/lib/jsonapi_plug/resource/validator.ex b/lib/jsonapi_plug/resource/validator.ex
new file mode 100644
index 00000000..74ac6ffd
--- /dev/null
+++ b/lib/jsonapi_plug/resource/validator.ex
@@ -0,0 +1,52 @@
+defprotocol JSONAPIPlug.Resource.Validator do
+  @moduledoc """
+  Resource Validator
+
+  Implement this protocol to validate a JSON:API resource.
+  Validation will be performed on resource attributes before normalizig them.
+
+  This example implementation always accepts params regardless of what is received.
+
+  ```elixir
+    defimpl JSONAPIPlug.Resource.Meta, for: MyApp.Post do
+      def validate(%@for{} = post, _params, _conn), do: :ok
+    end
+  ```
+  """
+
+  alias JSONAPIPlug.Document.{ErrorObject, ResourceObject}
+  alias JSONAPIPlug.Resource
+  alias Plug.Conn
+
+  @fallback_to_any true
+
+  @doc """
+  Validates the resource
+  """
+  @spec validate(Resource.t(), ResourceObject.attributes(), Conn.t()) ::
+          :ok | {:error, [ErrorObject.t()]}
+  def validate(resource, attributes, conn)
+end
+
+defimpl JSONAPIPlug.Resource.Validator, for: Any do
+  alias ExJsonSchema.Validator
+  alias JSONAPIPlug.Resource
+  alias JSONAPIPlug.Resource.Validator.ErrorFormatter
+  alias Plug.Conn
+
+  def validate(_resource, _attributes, %Conn{method: "PATCH"}), do: :ok
+
+  def validate(resource, attributes, %Conn{
+        private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
+      }) do
+    schema = Resource.schema(resource)
+
+    case Validator.validate(schema, attributes, error_formatter: false) do
+      :ok ->
+        :ok
+
+      {:error, errors} ->
+        {:error, ErrorFormatter.format(errors, resource, jsonapi_plug.config[:case])}
+    end
+  end
+end
diff --git a/lib/jsonapi_plug/resource/validator/error_formatter.ex b/lib/jsonapi_plug/resource/validator/error_formatter.ex
new file mode 100644
index 00000000..710aacf2
--- /dev/null
+++ b/lib/jsonapi_plug/resource/validator/error_formatter.ex
@@ -0,0 +1,25 @@
+defmodule JSONAPIPlug.Resource.Validator.ErrorFormatter do
+  @moduledoc false
+
+  alias ExJsonSchema.Validator.Error
+  alias JSONAPIPlug.Document.ErrorObject
+  alias JSONAPIPlug.Resource
+
+  def format(errors, resource, case) do
+    Enum.flat_map(errors, fn %Error{error: error, path: "#" <> path} ->
+      format_error(error, resource, case, "/data/attributes/" <> path)
+    end)
+  end
+
+  defp format_error(%Error.Required{} = error, resource, case, base_path) do
+    Enum.map(error.missing, fn attribute ->
+      %ErrorObject{
+        title: "Campo obbligatorio",
+        detail: "Questo campo è obbligatorio.",
+        status: 422,
+        code: :unprocessable_entity,
+        source: %{pointer: base_path <> Resource.recase_field(resource, attribute, case)}
+      }
+    end)
+  end
+end

From c59c07b656235069be06decf75feb6c269fddd12 Mon Sep 17 00:00:00 2001
From: Luca Corti <luca@fantacast.it>
Date: Thu, 3 Oct 2024 00:58:17 +0200
Subject: [PATCH 13/13] Cleanup

---
 lib/jsonapi_plug/resource/validator.ex | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/lib/jsonapi_plug/resource/validator.ex b/lib/jsonapi_plug/resource/validator.ex
index 74ac6ffd..7c712969 100644
--- a/lib/jsonapi_plug/resource/validator.ex
+++ b/lib/jsonapi_plug/resource/validator.ex
@@ -39,9 +39,7 @@ defimpl JSONAPIPlug.Resource.Validator, for: Any do
   def validate(resource, attributes, %Conn{
         private: %{jsonapi_plug: %JSONAPIPlug{} = jsonapi_plug}
       }) do
-    schema = Resource.schema(resource)
-
-    case Validator.validate(schema, attributes, error_formatter: false) do
+    case Validator.validate(Resource.schema(resource), attributes, error_formatter: false) do
       :ok ->
         :ok