From 5a0b68bd913ca816466d09431285c02373970406 Mon Sep 17 00:00:00 2001
From: Arun Sharma <arun@sharma-home.net>
Date: Wed, 29 Jan 2025 16:17:33 -0800
Subject: [PATCH] fquery.pydantic decorator

---
 fquery/pydantic.py     | 46 ++++++++++++++++++++++++++++++++++++++++++
 tests/test_pydantic.py | 34 +++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 fquery/pydantic.py
 create mode 100644 tests/test_pydantic.py

diff --git a/fquery/pydantic.py b/fquery/pydantic.py
new file mode 100644
index 0000000..810dcda
--- /dev/null
+++ b/fquery/pydantic.py
@@ -0,0 +1,46 @@
+import dataclasses
+from dataclasses import dataclass, fields
+from typing import Type
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+def pydantic(cls):
+    return model(dataclass(kw_only=True)(cls))
+
+
+def validator(self) -> BaseModel:
+    attrs = {name: getattr(self, name) for name in self.__pydantic__.model_fields}
+    return self.__pydantic__(**attrs)
+
+
+def get_field_def(cls, field):
+    # if the dataclass has a default_factory, or a default value, use it in pydantic Field
+    kwargs = {}
+    if not isinstance(field.default, dataclasses._MISSING_TYPE):
+        kwargs["default"] = field.default
+    if not isinstance(field.default_factory, dataclasses._MISSING_TYPE):
+        kwargs["default_factory"] = field.default_factory
+    return Field(**kwargs)
+
+
+def model(cls: Type) -> Type:
+    """
+    Decorator to convert a dataclass to a Pydantic model.
+    """
+    # Generate the SQLModel class
+    pydantic_cls = type(
+        cls.__name__ + "Model",
+        (BaseModel,),
+        {
+            # Add type annotations to the generated fields
+            "__annotations__": {**{field.name: field.type for field in fields(cls)}},
+            # Actual field defs
+            **{field.name: get_field_def(cls, field) for field in fields(cls)},
+        },
+    )
+    cls.__pydantic__ = pydantic_cls
+    cls.model_config = ConfigDict(extra="ignore")
+    cls.validator = validator
+
+    return cls
diff --git a/tests/test_pydantic.py b/tests/test_pydantic.py
new file mode 100644
index 0000000..27705c5
--- /dev/null
+++ b/tests/test_pydantic.py
@@ -0,0 +1,34 @@
+from dataclasses import is_dataclass
+
+import pytest
+from pydantic import BaseModel, ValidationError
+
+from fquery.pydantic import pydantic
+
+
+@pydantic
+class User:
+    name: str
+    age: int
+    is_active: bool = True
+
+
+def test_pydantic():
+    u1 = User(name="John Doe", age=42)
+    u2 = User(name="John Doe", age=42, is_active=False)
+    assert is_dataclass(u1)
+    assert is_dataclass(u2)
+
+    v1 = u1.validator()
+    v2 = u2.validator()
+    assert isinstance(v1, BaseModel)
+    assert isinstance(v2, BaseModel)
+
+    assert v1.model_dump() == u1.__dict__
+    assert v2.model_dump() == u2.__dict__
+
+
+def test_pydantic_fail():
+    u1 = User(name="John Doe", age=42.3)
+    with pytest.raises(ValidationError):
+        _ = u1.validator()