From 35335543850db28cde13dec4e8089f33d2063944 Mon Sep 17 00:00:00 2001
From: James Dibble <dibble.james@outlook.com>
Date: Wed, 23 Jul 2025 22:54:15 +0100
Subject: [PATCH] Project from an operation result

---
 LinQL.GraphQL.Client.Tests/QueryTests.cs      | 20 +++++++++++++++++++
 .../Translation/TranslationProviderTests.cs   | 14 +++++++++++++
 .../TranslationProviderTests.Project.snap     | 13 ++++++++++++
 ...iderTests.ProjectAcrossMultipleLevels.snap | 13 ++++++++++++
 ...sts.ProjectSameOperationMultipleTimes.snap | 14 +++++++++++++
 LinQL/SelectExtentions.cs                     | 10 ++++++++++
 6 files changed, 84 insertions(+)
 create mode 100644 LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.Project.snap
 create mode 100644 LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectAcrossMultipleLevels.snap
 create mode 100644 LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectSameOperationMultipleTimes.snap

diff --git a/LinQL.GraphQL.Client.Tests/QueryTests.cs b/LinQL.GraphQL.Client.Tests/QueryTests.cs
index eaa8f8f..5462cc7 100644
--- a/LinQL.GraphQL.Client.Tests/QueryTests.cs
+++ b/LinQL.GraphQL.Client.Tests/QueryTests.cs
@@ -42,6 +42,16 @@ public async Task TestSendQuery()
         result.Data.Should().Be(12345);
     }
 
+    [Fact]
+    public async Task TestSendProjectionQuery()
+    {
+        var result = await this.client.SendAsync((TestQuery q) => q.ExecuteEchoOperation("echo").Project(e => new { e.Echo, e.Number }));
+
+        result.Errors.Should().BeNull();
+        result.Data.Number.Should().Be(42);
+        result.Data.Echo.Should().Be("echo");
+    }
+
     [Fact]
     public async Task TestSendMutation()
     {
@@ -60,8 +70,12 @@ public void Dispose()
     public class TestQueryType
     {
         public int GetNumber() => 12345;
+
+        public TestObjectType EchoOperation(string toEcho) => new(toEcho, 42);
     }
 
+    public record TestObjectType(string Echo, int Number);
+
     public class TestMutationType
     {
         public NumberResult SetNumber([GraphQLArgument(GQLType = "Int")] int input) => new() { Number = input };
@@ -79,6 +93,12 @@ public class TestQuery : RootType<TestQuery>
 
         [GraphQLOperation, GraphQLField(Name = "number")]
         public int GetNumber() => this.Number;
+
+        [GraphQLOperation, GraphQLField(Name = "echoOperation")]
+        public TestObjectType ExecuteEchoOperation([GraphQLArgument(GQLType = "String!")] string toEcho)
+            => this.EchoOperation;
+
+        public TestObjectType EchoOperation { get; set; }
     }
 
     [OperationType(RootOperationType.Mutation)]
diff --git a/LinQL.Tests/Translation/TranslationProviderTests.cs b/LinQL.Tests/Translation/TranslationProviderTests.cs
index ebaa370..cdd0911 100644
--- a/LinQL.Tests/Translation/TranslationProviderTests.cs
+++ b/LinQL.Tests/Translation/TranslationProviderTests.cs
@@ -181,6 +181,8 @@ public void SelectInterfaceArrayMultipleTypesSelectAll()
 
     private record Projection(int Number, string? Text);
 
+    private record NestedProjection(float Float, Projection Projection);
+
     [Fact]
     public void ProjectArrayOfInterface()
         => this.Test<InterfaceRootType, object>(x => x.ArrayOfInterfaces.Select(a => new Projection(a.Number, a.Text)));
@@ -205,6 +207,18 @@ private void TestInclude<TRoot, TData>(Expression<Func<TRoot, TData>> expression
         Snapshot.Match(request.Query);
     }
 
+    [Fact]
+    public void Project()
+        => this.Test<NestedOperationType, Projection>(x => x.Operation.GetNumber("project me").Project(y => new Projection(y.Number, y.Text)));
+
+    [Fact]
+    public void ProjectAcrossMultipleLevels()
+        => this.Test<NestedOperationType, Projection>(x => new Projection(x.Number, x.Operation.GetNumber("project me").Project(y => y.Text)));
+
+    [Fact]
+    public void ProjectSameOperationMultipleTimes()
+        => this.Test<NestedOperationType, NestedProjection>(x => new NestedProjection(x.Operation.Float, x.Operation.GetNumber("project me").Project(y => new Projection(y.Number, y.Text))));
+
     private void Test<TRoot, TData>(Expression<Func<TRoot, TData>> expression)
         where TRoot : RootType<TRoot>
         => this.TestInclude(expression, _ => { });
diff --git a/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.Project.snap b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.Project.snap
new file mode 100644
index 0000000..7a3466c
--- /dev/null
+++ b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.Project.snap
@@ -0,0 +1,13 @@
+query linql(
+  $var1: String!
+)
+ {
+  operation {
+    getNumber(
+      value: $var1
+    ) {
+      number
+      text
+    }
+  }
+}
diff --git a/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectAcrossMultipleLevels.snap b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectAcrossMultipleLevels.snap
new file mode 100644
index 0000000..dd77c15
--- /dev/null
+++ b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectAcrossMultipleLevels.snap
@@ -0,0 +1,13 @@
+query linql(
+  $var1: String!
+)
+ {
+  number
+  operation {
+    getNumber(
+      value: $var1
+    ) {
+      text
+    }
+  }
+}
diff --git a/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectSameOperationMultipleTimes.snap b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectSameOperationMultipleTimes.snap
new file mode 100644
index 0000000..b818a26
--- /dev/null
+++ b/LinQL.Tests/Translation/__snapshots__/TranslationProviderTests.ProjectSameOperationMultipleTimes.snap
@@ -0,0 +1,14 @@
+query linql(
+  $var1: String!
+)
+ {
+  operation {
+    float
+    getNumber(
+      value: $var1
+    ) {
+      number
+      text
+    }
+  }
+}
diff --git a/LinQL/SelectExtentions.cs b/LinQL/SelectExtentions.cs
index 8e44ed6..deeab67 100644
--- a/LinQL/SelectExtentions.cs
+++ b/LinQL/SelectExtentions.cs
@@ -60,4 +60,14 @@ public static OneOf<T, TResult> On<T, TMaybe, TResult>(this OneOf<T, TResult> th
     /// <param name="that">The type.</param>
     /// <returns>The type.</returns>
     public static T SelectAll<T>(this T that) => that;
+
+    /// <summary>
+    /// Instruct the query to get all scalar fields on this type.
+    /// </summary>
+    /// <typeparam name="T">The type to select from.</typeparam>
+    /// <typeparam name="TResult">The type to project to.</typeparam>
+    /// <param name="that">The type.</param>
+    /// <param name="projection">The expression required to create <typeparamref name="TResult"/> from <typeparamref name="T"/>.</param>
+    /// <returns>The projection.</returns>
+    public static TResult Project<T, TResult>(this T that, Expression<Func<T, TResult>> projection) => projection.CompileFast()(that);
 }