Repository: microsoft/kiota (csharp)

Issue:
Models with discriminator get superfluous fields
I have a simple model that can of two types: A or B, like what's shown in the spec below.

```yaml
openapi: 3.0.3
info:
  title: Example API
  version: 1.0.0
servers:
  - url: "https://localhost:8080"
paths:
  "/api/all":
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/AorB"
        required: true
      responses:
        "200":
          $ref: "#/components/responses/AorBResponse"
components:
  schemas:
    A:
      type: object
      required:
        - type
      properties:
        type:
          type: string
          default: "a"
    B:
      type: object
      required:
        - type
      properties:
        type:
          type: string
          default: "b"
    AorB:
      oneOf:
        - $ref: "#/components/schemas/A"
        - $ref: "#/components/schemas/B"
      discriminator:
        propertyName: type
        mapping:
          a: "#/components/schemas/A"
          b: "#/components/schemas/B"
  responses:
    AorBResponse:
      description: mandatory
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/AorB"
```

When I try to generate code (tested with both Python and Go), I get some superfluous values and unnecessary checks. e.g. in Python:

```py
from __future__ import annotations
from dataclasses import dataclass, field
from kiota_abstractions.serialization import Parsable, ParseNode, SerializationWriter
from kiota_abstractions.serialization.composed_type_wrapper import ComposedTypeWrapper
from typing import Any, Callable, Dict, List, Optional, TYPE_CHECKING, Union

if TYPE_CHECKING:
    from .a import A
    from .b import B

@dataclass
class AorB(ComposedTypeWrapper, Parsable):
    """
    Composed type wrapper for classes A, B
    """
    @staticmethod
    def create_from_discriminator_value(parse_node: Optional[ParseNode] = None) -> AorB:
        """
        Creates a new instance of the appropriate class based on discriminator value
        param parse_node: The parse node to use to read the discriminator value and create the object
        Returns: AorB
        """
        if not parse_node:
            raise TypeError("parse_node cannot be null.")
        try:
            mapping_value = parse_node.get_child_node("type").get_str_value()
        except AttributeError:
            mapping_value = None
        result = AorB()
        if mapping_value and mapping_value.casefold() == "a".casefold():
            from .a import A

            result.a = A()
        elif mapping_value and mapping_value.casefold() == "a".casefold():
            from .a import A

            result.aor_b_a = A()
        elif mapping_value and mapping_value.casefold() == "a".casefold():
            from .a import A

            result.aor_b_a0 = A()
        elif mapping_value and mapping_value.casefold() == "b".casefold():
            from .b import B

            result.aor_b_b = B()
        elif mapping_value and mapping_value.casefold() == "b".casefold():
            from .b import B

            result.aor_b_b0 = B()
        elif mapping_value and mapping_value.casefold() == "b".casefold():
            from .b import B

            result.b = B()
        return result
    
    def get_field_deserializers(self,) -> Dict[str, Callable[[ParseNode], None]]:
        """
        The deserialization information for the current model
        Returns: Dict[str, Callable[[ParseNode], None]]
        """
        from .a import A
        from .b import B

        if self.a:
            return self.a.get_field_deserializers()
        if self.aor_b_a:
            return self.aor_b_a.get_field_deserializers()
        if self.aor_b_a0:
            return self.aor_b_a0.get_field_deserializers()
        if self.aor_b_b:
            return self.aor_b_b.get_field_deserializers()
        if self.aor_b_b0:
            return self.aor_b_b0.get_field_deserializers()
        if self.b:
            return self.b.get_field_deserializers()
        return {}
    
    def serialize(self,writer: SerializationWriter) -> None:
        """
        Serializes information the current object
        param writer: Serialization writer to use to serialize this model
        Returns: None
        """
        if not writer:
            raise TypeError("writer cannot be null.")
        if self.a:
            writer.write_object_value(None, self.a)
        elif self.aor_b_a:
            writer.write_object_value(None, self.aor_b_a)
        elif self.aor_b_a0:
            writer.write_object_value(None, self.aor_b_a0)
        elif self.aor_b_b:
            writer.write_object_value(None, self.aor_b_b)
        elif self.aor_b_b0:
            writer.write_object_value(None, self.aor_b_b0)
        elif self.b:
            writer.write_object_value(None, self.b)
```

Ideally, the A or B type should simply correspond to something like

```py
class AorB(BaseModel):
    a: A | None
    b: B | None
```

that is, without any superfluous fields.

Pull request description:
Fixes https://github.com/microsoft/kiota/issues/4178
Fixes https://github.com/microsoft/kiota/issues/4478

In the event that a union type was converted to a wrapper type, the CommonLanguage refiner would not check if the type was already present in the namespace. It therefore went ahead to add the same properties over and over whenever `ConvertComposedTypeToWrapper` is called.

Patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e17050735e..7327f1b128 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed a bug where composed types wrappers would not build in CSharp.
 - Fixed a bug where the type name for inherited inline models would be incorrect. [#5610](https://github.com/microsoft/kiota/issues/5610)
 - Fixes typing inconsistencies in generated code and libraries in Python [kiota-python#333](https://github.com/microsoft/kiota-python/issues/333)
+- Fixes generation of superfluous fields for Models with discriminator due to refiners adding the same properties to the same model [#4178](https://github.com/microsoft/kiota/issues/4178).
 
 ## [1.19.1] - 2024-10-11
 
diff --git a/src/Kiota.Builder/Refiners/CommonLanguageRefiner.cs b/src/Kiota.Builder/Refiners/CommonLanguageRefiner.cs
index 5289f6546f..6cdaebe093 100644
--- a/src/Kiota.Builder/Refiners/CommonLanguageRefiner.cs
+++ b/src/Kiota.Builder/Refiners/CommonLanguageRefiner.cs
@@ -485,8 +485,10 @@ private static CodeType ConvertComposedTypeToWrapper(CodeClass codeClass, CodeCo
         if (!supportsInnerClasses)
         {
             var @namespace = codeClass.GetImmediateParentOfType<CodeNamespace>();
-            if (@namespace.FindChildByName<CodeClass>(codeComposedType.Name, false) is CodeClass { OriginalComposedType: null })
+            if (@namespace.FindChildByName<CodeClass>(codeComposedType.Name, false) is { OriginalComposedType: null })
                 codeComposedType.Name = $"{codeComposedType.Name}Wrapper";
+            if (GetAlreadyExistingComposedCodeType(@namespace, codeComposedType) is { } existingCodeType)
+                return existingCodeType;
             newClass = @namespace.AddClass(new CodeClass
             {
                 Name = codeComposedType.Name,
@@ -499,8 +501,10 @@ private static CodeType ConvertComposedTypeToWrapper(CodeClass codeClass, CodeCo
                 Deprecation = codeComposedType.Deprecation,
             }).Last();
         }
-        else if (codeComposedType.TargetNamespace is CodeNamespace targetNamespace)
+        else if (codeComposedType.TargetNamespace is { } targetNamespace)
         {
+            if (GetAlreadyExistingComposedCodeType(targetNamespace, codeComposedType) is { } existingCodeType)
+                return existingCodeType;
             newClass = targetNamespace.AddClass(new CodeClass
             {
                 Name = codeComposedType.Name,
@@ -523,6 +527,8 @@ private static CodeType ConvertComposedTypeToWrapper(CodeClass codeClass, CodeCo
         {
             if (codeComposedType.Name.Equals(codeClass.Name, StringComparison.OrdinalIgnoreCase) || codeClass.FindChildByName<CodeProperty>(codeComposedType.Name, false) is not null)
                 codeComposedType.Name = $"{codeComposedType.Name}Wrapper";
+            if (GetAlreadyExistingComposedCodeType(codeClass, codeComposedType) is { } existingCodeType)
+                return existingCodeType;
             newClass = codeClass.AddInnerClass(new CodeClass
             {
                 Name = codeComposedType.Name,
@@ -602,6 +608,24 @@ private static CodeType ConvertComposedTypeToWrapper(CodeClass codeClass, CodeCo
             ActionOf = codeComposedType.ActionOf,
         };
     }
+
+    private static CodeType? GetAlreadyExistingComposedCodeType(IBlock targetNamespace, CodeComposedTypeBase codeComposedType)
+    {
+        if (targetNamespace.FindChildByName<CodeClass>(codeComposedType.Name, false) is { OriginalComposedType: not null } existingClass && existingClass.OriginalComposedType.Name.Equals(codeComposedType.Name, StringComparison.OrdinalIgnoreCase))
+        { // the composed type was already added/created and the typeDefinition(codeclass) is already present in the namespace/class.
+            return new CodeType
+            {
+                Name = codeComposedType.Name,
+                TypeDefinition = existingClass,
+                CollectionKind = codeComposedType.CollectionKind,
+                IsNullable = codeComposedType.IsNullable,
+                ActionOf = codeComposedType.ActionOf,
+            };
+        }
+
+        return null;
+    }
+
     protected static void MoveClassesWithNamespaceNamesUnderNamespace(CodeElement currentElement)
     {
         if (currentElement is CodeClass currentClass &&


Test patch:
diff --git a/tests/Kiota.Builder.Tests/KiotaBuilderTests.cs b/tests/Kiota.Builder.Tests/KiotaBuilderTests.cs
index b1c6dcc045..606bbe5c62 100644
--- a/tests/Kiota.Builder.Tests/KiotaBuilderTests.cs
+++ b/tests/Kiota.Builder.Tests/KiotaBuilderTests.cs
@@ -581,6 +581,103 @@ public async Task DoesntConflictOnModelsNamespaceAsync()
         Assert.NotNull(innerRequestBuilderNS.FindChildByName<CodeClass>("InnerRequestBuilder", false));
 
     }
+    [Theory]
+    [InlineData(GenerationLanguage.CSharp)]
+    [InlineData(GenerationLanguage.Java)]
+    [InlineData(GenerationLanguage.TypeScript)]
+    [InlineData(GenerationLanguage.Python)]
+    [InlineData(GenerationLanguage.Go)]
+    [InlineData(GenerationLanguage.PHP)]
+    [InlineData(GenerationLanguage.Ruby)]
+    public async Task DoesNotAddSuperflousFieldsToModelsAsync(GenerationLanguage language)
+    {
+        var tempFilePath = Path.Combine(Path.GetTempPath(), Path.GetTempFileName());
+        await using var fs = await GetDocumentStreamAsync(@"openapi: 3.0.3
+info:
+  title: Example API
+  version: 1.0.0
+servers:
+  - url: ""https://localhost:8080""
+paths:
+  ""/api/all"":
+    post:
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: ""#/components/schemas/AorB""
+        required: true
+      responses:
+        ""200"":
+          $ref: ""#/components/responses/AorBResponse""
+components:
+  schemas:
+    A:
+      type: object
+      required:
+        - type
+      properties:
+        type:
+          type: string
+          default: ""a""
+    B:
+      type: object
+      required:
+        - type
+      properties:
+        type:
+          type: string
+          default: ""b""
+    AorB:
+      oneOf:
+        - $ref: ""#/components/schemas/A""
+        - $ref: ""#/components/schemas/B""
+      discriminator:
+        propertyName: type
+        mapping:
+          a: ""#/components/schemas/A""
+          b: ""#/components/schemas/B""
+  responses:
+    AorBResponse:
+      description: mandatory
+      content:
+        application/json:
+          schema:
+            $ref: ""#/components/schemas/AorB""");
+        var mockLogger = new Mock<ILogger<KiotaBuilder>>();
+        var generationConfiguration = new GenerationConfiguration { ClientClassName = "Graph", OpenAPIFilePath = tempFilePath, Language = language }; // we can use any language that creates wrapper types for composed types in different ways
+        var builder = new KiotaBuilder(mockLogger.Object, generationConfiguration, _httpClient);
+        var document = await builder.CreateOpenApiDocumentAsync(fs);
+        var node = builder.CreateUriSpace(document);
+        var codeModel = builder.CreateSourceModel(node);
+        await builder.ApplyLanguageRefinementAsync(generationConfiguration, codeModel, CancellationToken.None);
+        var requestBuilderNamespace = codeModel.FindNamespaceByName("ApiSdk.api.all");
+        Assert.NotNull(requestBuilderNamespace);
+        if (language == GenerationLanguage.TypeScript || language == GenerationLanguage.Go)
+        {// these languages use CodeFiles
+            var requestExecutorMethod = codeModel.FindChildByName<CodeMethod>("post");
+            Assert.NotNull(requestExecutorMethod);
+            var returnType = requestExecutorMethod.ReturnType as CodeType;
+            var returnTypeDefinition = returnType.TypeDefinition as CodeInterface;
+            if (language == GenerationLanguage.TypeScript)
+            {
+                Assert.Equal(2, returnTypeDefinition.Properties.Count());
+            }
+            if (language == GenerationLanguage.Go)
+            {
+                Assert.Equal(4, returnTypeDefinition.Methods.Count());// a getter and a setter for each property in Go.
+            }
+        }
+        else
+        {
+            var allRequestBuilderClass = requestBuilderNamespace.FindChildByName<CodeClass>("allRequestBuilder", false);
+            var executor = allRequestBuilderClass.Methods.FirstOrDefault(m => m.IsOfKind(CodeMethodKind.RequestExecutor));
+            Assert.NotNull(executor);
+            var returnType = executor.ReturnType as CodeType;
+            var returnTypeDefinition = returnType.TypeDefinition as CodeClass;
+            Assert.Equal(2, returnTypeDefinition.Properties.Count());
+        }
+    }
     [Fact]
     public async Task NamesComponentsInlineSchemasProperlyAsync()
     {