Feat/add support default mapping

src/Microsoft.OpenApi/Models/OpenApiDiscriminator.cs

@@ -25,6 +25,11 @@ public class OpenApiDiscriminator : IOpenApiSerializable, IOpenApiExtensible
         /// </summary>
         public IDictionary<string, IOpenApiExtension>? Extensions { get; set; }
 
+        /// <summary>
+        /// OAI 3.2.0: The schema name or URI reference to a schema that is expected to validate the structure of the model when the discriminating property is not present in the payload or contains a value for which there is no explicit or implicit mapping.
+        /// </summary>
+        public OpenApiSchemaReference? DefaultMapping { get; set; }
+
         /// <summary>
         /// Parameter-less constructor
         /// </summary>
@@ -38,6 +43,7 @@ public OpenApiDiscriminator(OpenApiDiscriminator discriminator)
             PropertyName = discriminator?.PropertyName ?? PropertyName;
             Mapping = discriminator?.Mapping != null ? new Dictionary<string, OpenApiSchemaReference>(discriminator.Mapping) : null;
             Extensions = discriminator?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(discriminator.Extensions) : null;
+            DefaultMapping = discriminator?.DefaultMapping;
         }
 
         /// <summary>
@@ -48,6 +54,13 @@ public void SerializeAsV32(IOpenApiWriter writer)
         {
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_2);
 
+            // Write defaultMapping property in 3.2.0
+            if (DefaultMapping != null)
+            {
+                writer.WritePropertyName("defaultMapping");
+                DefaultMapping.SerializeAsV32(writer);
+            }
+
             // extensions
             writer.WriteExtensions(Extensions, OpenApiSpecVersion.OpenApi3_2);
 
@@ -62,6 +75,13 @@ public void SerializeAsV31(IOpenApiWriter writer)
         {
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_1);
 
+            // Write as x-oas-default-mapping extension in 3.1.0
+            if (DefaultMapping != null)
+            {
+                writer.WritePropertyName("x-oas-default-mapping");
+                DefaultMapping.SerializeAsV31(writer);
+            }
+
             // extensions
             writer.WriteExtensions(Extensions, OpenApiSpecVersion.OpenApi3_1);
 
@@ -75,6 +95,13 @@ public void SerializeAsV3(IOpenApiWriter writer)
         {
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_0);
 
+            // Write as x-oas-default-mapping extension in 3.0.0
+            if (DefaultMapping != null)
+            {
+                writer.WritePropertyName("x-oas-default-mapping");
+                DefaultMapping.SerializeAsV3(writer);
+            }
+
             writer.WriteEndObject();
         }
 

src/Microsoft.OpenApi/Reader/V3/OpenApiDiscriminatorDeserializer.cs

@@ -24,7 +24,16 @@ internal static partial class OpenApiV3Deserializer
                 }
             };
 
-        private static readonly PatternFieldMap<OpenApiDiscriminator> _discriminatorPatternFields = new();
+        private static readonly PatternFieldMap<OpenApiDiscriminator> _discriminatorPatternFields = new() {
+                {s => s.StartsWith(OpenApiConstants.ExtensionFieldNamePrefix, StringComparison.OrdinalIgnoreCase), (o, p, n, doc) => {
+                        // Handle x-oas-default-mapping as DefaultMapping property
+                        if (p.Equals("x-oas-default-mapping", StringComparison.OrdinalIgnoreCase))
+                        {
+                            o.DefaultMapping = LoadMapping(n, doc);
+                        }
+                    }
+                }
+            };
 
         public static OpenApiDiscriminator LoadDiscriminator(ParseNode node, OpenApiDocument hostDocument)
         {

src/Microsoft.OpenApi/Reader/V31/OpenApiDiscriminatorDeserializer.cs

@@ -28,7 +28,18 @@ internal static partial class OpenApiV31Deserializer
         private static readonly PatternFieldMap<OpenApiDiscriminator> _discriminatorPatternFields =
             new()
             {
-                {s => s.StartsWith(OpenApiConstants.ExtensionFieldNamePrefix, StringComparison.OrdinalIgnoreCase), (o, p, n, _) => o.AddExtension(p, LoadExtension(p,n))}
+                {s => s.StartsWith(OpenApiConstants.ExtensionFieldNamePrefix, StringComparison.OrdinalIgnoreCase), (o, p, n, doc) => {
+                        // Handle x-oas-default-mapping as DefaultMapping property
+                        if (p.Equals("x-oas-default-mapping", StringComparison.OrdinalIgnoreCase))
+                        {
+                            o.DefaultMapping = LoadMapping(n, doc);
+                        }
+                        else
+                        {
+                            o.AddExtension(p, LoadExtension(p, n));
+                        }
+                    }
+                }
             };
 
         public static OpenApiDiscriminator LoadDiscriminator(ParseNode node, OpenApiDocument hostDocument)

src/Microsoft.OpenApi/Reader/V32/OpenApiDiscriminatorDeserializer.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 
 namespace Microsoft.OpenApi.Reader.V32
 {
@@ -22,6 +22,12 @@ internal static partial class OpenApiV32Deserializer
                     {
                         o.Mapping = n.CreateSimpleMap((node) => LoadMapping(node, doc));
                     }
+                },
+                 {
+                    "defaultMapping", (o, n, doc) =>
+                    {
+                        o.DefaultMapping = LoadMapping(n, doc);
+                    }
                 }
             };
 

test/Microsoft.OpenApi.Readers.Tests/V31Tests/OpenApiDiscriminatorTests.cs

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.OpenApi.Reader;
+using Xunit;
+
+namespace Microsoft.OpenApi.Readers.Tests.V31Tests
+{
+    [Collection("DefaultSettings")]
+    public class OpenApiDiscriminatorTests
+    {
+        private const string SampleFolderPath = "V31Tests/Samples/OpenApiDiscriminator/";
+
+        [Fact]
+        public async Task ParseBasicDiscriminatorShouldSucceed()
+        {
+            // Arrange
+            using var stream = Resources.GetStream(Path.Combine(SampleFolderPath, "basicDiscriminator.yaml"));
+            // Copy stream to MemoryStream
+            using var memoryStream = new MemoryStream();
+            await stream.CopyToAsync(memoryStream);
+            memoryStream.Position = 0;
+
+            // Act
+            var openApiDocument = new OpenApiDocument();
+            var discriminator = OpenApiModelFactory.Load<OpenApiDiscriminator>(memoryStream, OpenApiSpecVersion.OpenApi3_1, OpenApiConstants.Yaml, openApiDocument, out var diagnostic, SettingsFixture.ReaderSettings);
+
+            // Assert
+            Assert.Equivalent(
+               new OpenApiDiscriminator
+               {
+                   PropertyName = "pet_type",
+                   Mapping = new Dictionary<string, OpenApiSchemaReference>
+                   {
+                            ["puppy"] = new OpenApiSchemaReference("Dog", openApiDocument),
+                            ["kitten"] = new OpenApiSchemaReference("Cat" , openApiDocument, "https://gigantic-server.com/schemas/animals.json"),
+                            ["monster"] = new OpenApiSchemaReference("monster" , openApiDocument, "https://gigantic-server.com/schemas/Monster/schema.json")
+                    },
+                   DefaultMapping = new OpenApiSchemaReference("Animal", openApiDocument)  
+               }, discriminator);
+        }
+    }
+}

test/Microsoft.OpenApi.Readers.Tests/V31Tests/Samples/OpenApiDiscriminator/basicDiscriminator.yaml

@@ -0,0 +1,6 @@
+propertyName: pet_type
+mapping:
+    puppy: '#/components/schemas/Dog'
+    kitten: https://gigantic-server.com/schemas/animals.json#/components/schemas/Cat
+    monster: https://gigantic-server.com/schemas/Monster/schema.json#/components/schemas/monster
+x-oas-default-mapping: '#/components/schemas/Animal'

test/Microsoft.OpenApi.Readers.Tests/V32Tests/OpenApiDiscriminatorTests.cs

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.OpenApi.Reader;
+using Xunit;
+
+namespace Microsoft.OpenApi.Readers.Tests.V32Tests
+{
+    [Collection("DefaultSettings")]
+    public class OpenApiDiscriminatorTests
+    {
+        private const string SampleFolderPath = "V32Tests/Samples/OpenApiDiscriminator/";
+
+        [Fact]
+        public async Task ParseBasicDiscriminatorShouldSucceed()
+        {
+            // Arrange
+            using var stream = Resources.GetStream(Path.Combine(SampleFolderPath, "basicDiscriminator.yaml"));
+            // Copy stream to MemoryStream
+            using var memoryStream = new MemoryStream();
+            await stream.CopyToAsync(memoryStream);
+            memoryStream.Position = 0;
+
+            // Act
+            var openApiDocument = new OpenApiDocument();
+            var discriminator = OpenApiModelFactory.Load<OpenApiDiscriminator>(memoryStream, OpenApiSpecVersion.OpenApi3_2, OpenApiConstants.Yaml, openApiDocument, out var diagnostic, SettingsFixture.ReaderSettings);
+
+            // Assert
+            Assert.Equivalent(
+               new OpenApiDiscriminator
+               {
+                   PropertyName = "pet_type",
+                   Mapping = new Dictionary<string, OpenApiSchemaReference>
+                   {
+                            ["puppy"] = new OpenApiSchemaReference("Dog", openApiDocument),
+                            ["kitten"] = new OpenApiSchemaReference("Cat" , openApiDocument, "https://gigantic-server.com/schemas/animals.json"),
+                            ["monster"] = new OpenApiSchemaReference("monster" , openApiDocument, "https://gigantic-server.com/schemas/Monster/schema.json")
+                    },
+                   DefaultMapping = new OpenApiSchemaReference("Animal", openApiDocument)
+               }, discriminator);
+        }
+    }
+}

test/Microsoft.OpenApi.Readers.Tests/V32Tests/Samples/OpenApiDiscriminator/basicDiscriminator.yaml

@@ -0,0 +1,6 @@
+propertyName: pet_type
+mapping:
+    puppy: '#/components/schemas/Dog'
+    kitten: https://gigantic-server.com/schemas/animals.json#/components/schemas/Cat
+    monster: https://gigantic-server.com/schemas/Monster/schema.json#/components/schemas/monster
+defaultMapping: '#/components/schemas/Animal'

test/Microsoft.OpenApi.Readers.Tests/V3Tests/OpenApiDiscriminatorTests.cs

@@ -38,7 +38,8 @@ public async Task ParseBasicDiscriminatorShouldSucceed()
                             ["puppy"] = new OpenApiSchemaReference("Dog", openApiDocument),
                             ["kitten"] = new OpenApiSchemaReference("Cat" , openApiDocument, "https://gigantic-server.com/schemas/animals.json"),
                             ["monster"] = new OpenApiSchemaReference("schema.json" , openApiDocument, "https://gigantic-server.com/schemas/Monster/schema.json")
-                    }
+                    },
+                   DefaultMapping = new OpenApiSchemaReference("Animal", openApiDocument)
                }, discriminator);
         }
     }

test/Microsoft.OpenApi.Readers.Tests/V3Tests/Samples/OpenApiDiscriminator/basicDiscriminator.yaml

@@ -2,4 +2,5 @@
 mapping:
     puppy: '#/components/schemas/Dog'
     kitten: https://gigantic-server.com/schemas/animals.json#/components/schemas/Cat
-    monster: https://gigantic-server.com/schemas/Monster/schema.json
+    monster: https://gigantic-server.com/schemas/Monster/schema.json
+x-oas-default-mapping: '#/components/schemas/Animal'

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -594,6 +594,7 @@ namespace Microsoft.OpenApi
     {
         public OpenApiDiscriminator() { }
         public OpenApiDiscriminator(Microsoft.OpenApi.OpenApiDiscriminator discriminator) { }
+        public Microsoft.OpenApi.OpenApiSchemaReference? DefaultMapping { get; set; }
         public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.IOpenApiExtension>? Extensions { get; set; }
         public System.Collections.Generic.IDictionary<string, Microsoft.OpenApi.OpenApiSchemaReference>? Mapping { get; set; }
         public string? PropertyName { get; set; }