Adds mapping object to discriminator objects

src/Microsoft.OpenApi.OData.Reader/Generator/OpenApiSchemaGenerator.cs

@@ -430,9 +430,22 @@ private static OpenApiSchema CreateStructuredTypeSchema(this ODataContext contex
                 OpenApiDiscriminator discriminator = null;
                 if (context.Settings.EnableDiscriminatorValue && derivedTypes.Any() && structuredType.BaseType != null)
                 {
+                    string v3RefIdentifier = new OpenApiSchema
+                    {
+                        Reference = new OpenApiReference
+                        {
+                            Type = ReferenceType.Schema,
+                            Id = structuredType.FullTypeName()
+                        }
+                    }.Reference.ReferenceV3;
+
                     discriminator = new OpenApiDiscriminator
                     {
-                        PropertyName = "@odata.type"
+                        PropertyName = "@odata.type",
+                        Mapping = new Dictionary<string, string>
+                        {
+                            {"#" + structuredType.FullTypeName(), v3RefIdentifier }
+                        }
                     };
                 }
 

test/Microsoft.OpenAPI.OData.Reader.Tests/Generator/OpenApiSchemaGeneratorTests.cs

@@ -80,6 +80,52 @@ public void CreateStructuredTypeSchemaThrowArgumentNullEnumType()
             Assert.Throws<ArgumentNullException>("structuredType", () => context.CreateStructuredTypeSchema(structuredType: null));
         }
 
+        [Fact]
+        public void CreateStructuredTypeSchemaWithDiscriminatorValueEnabledReturnsCorrectSchema()
+        {
+            // Arrange
+            IEdmModel model = EdmModelHelper.GraphBetaModel;
+            ODataContext context = new(model, new OpenApiConvertSettings
+            {
+                EnableDiscriminatorValue = true,
+            });
+
+            IEdmEntityType entity = model.SchemaElements.OfType<IEdmEntityType>().First(t => t.Name == "directoryObject");
+            Assert.NotNull(entity); // Guard
+
+            // Act
+            var schema = context.CreateStructuredTypeSchema(entity);
+            string json = schema.SerializeAsJson(OpenApiSpecVersion.OpenApi3_0);
+
+            // Assert
+            Assert.NotNull(json);
+            Assert.Equal(@"{
+  ""allOf"": [
+    {
+      ""$ref"": ""#/components/schemas/microsoft.graph.entity""
+    },
+    {
+      ""title"": ""directoryObject"",
+      ""type"": ""object"",
+      ""properties"": {
+        ""deletedDateTime"": {
+          ""pattern"": ""^[0-9]{4,}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])T([01][0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9]([.][0-9]{1,12})?(Z|[+-][0-9][0-9]:[0-9][0-9])$"",
+          ""type"": ""string"",
+          ""format"": ""date-time"",
+          ""nullable"": true
+        }
+      },
+      ""discriminator"": {
+        ""propertyName"": ""@odata.type"",
+        ""mapping"": {
+          ""#microsoft.graph.directoryObject"": ""#/components/schemas/microsoft.graph.directoryObject""
+        }
+      }
+    }
+  ]
+}".ChangeLineBreaks(), json);
+        }
+
         [Fact]
         public void CreateComplexTypeWithoutBaseSchemaReturnCorrectSchema()
         {