Multiple identical classes are generated for a component schema with allOf inheritance

[bkoelman]

When using inheritance using allOf, Kiota generates multiple identical classes for the same component schema. As a result, the types are incompatible when trying to consume the C# code generated by Kiota.

I've tried to create a minimal repro, but the OAS is still quite large. The full file is provided below. At a high level, the structure contains the following base component schema:

"dataInResponse": {
  "required": [
    "id",
    "type"
  ],
  "type": "object",
  "properties": {
    "type": {
      "minLength": 1,
      "type": "string"
    },
    "id": {
      "minLength": 1,
      "type": "string"
    }
  },
  "additionalProperties": false,
  "discriminator": {
    "propertyName": "type",
    "mapping": {
      "tags": "#/components/schemas/tagDataInResponse",
      "todoItems": "#/components/schemas/todoItemDataInResponse"
    }
  },
  "x-abstract": true
}

with derived schemas tagDataInResponse and todoItemDataInResponse, ie:

"todoItemDataInResponse": {
  "allOf": [
    {
      "$ref": "#/components/schemas/dataInResponse"
    },
    {
      "type": "object",
      "properties": {
        "attributes": {
          "allOf": [
            {
              "$ref": "#/components/schemas/todoItemAttributesInResponse"
            }
          ]
        },
        "relationships": {
          "allOf": [
            {
              "$ref": "#/components/schemas/todoItemRelationshipsInResponse"
            }
          ]
        }
      },
      "additionalProperties": false
    }
  ],
  "additionalProperties": false
}

These schemas are used from two GET endpoints, one returning a collection and the other a singular item. The response schema in both cases contains a data property (derived schema reference, or an array of that) and an included property (array of base schema reference).

The first endpoint (paths./api/todoItems.get) uses the following response schema:

"todoItemCollectionResponseDocument": {
  "required": [
    "data"
  ],
  "type": "object",
  "properties": {
    "data": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/todoItemDataInResponse"
      }
    },
    "included": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/dataInResponse"
      }
    }
  },
  "additionalProperties": false
}

And the second endpoint (paths./api/todoItems/{id}.get) uses the following schema:

"todoItemPrimaryResponseDocument": {
  "required": [
    "data"
  ],
  "type": "object",
  "properties": {
    "data": {
      "allOf": [
        {
          "$ref": "#/components/schemas/todoItemDataInResponse"
        }
      ]
    },
    "included": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/dataInResponse"
      }
    }
  },
  "additionalProperties": false
}

I would have expected Kiota to generate the base class DataInResponse, with the two derived classes TodoItemDataInResponse and TagDataInResponse. What happens is that Kiota also generates the derived class TodoItems, whose content is identical to TodoItemDataInResponse. The unexpected TodoItems class is only used by the singular endpoint.

As a result, it's not possible to define a method that takes a parameter of type TodoItemDataInResponse and is called with the response from both endpoints. I would have expected to be able to write:

TodoItemPrimaryResponseDocument? getSingleResponse = await client.Api.TodoItems["1"].GetAsync();
PrintTodoItem(getSingleResponse!.Data!, getSingleResponse.Included);

TodoItemCollectionResponseDocument? getMultiResponse = await client.Api.TodoItems.GetAsync();
foreach (TodoItemDataInResponse todoItem in getMultiResponse!.Data!)
{
    PrintTodoItem(todoItem, getMultiResponse.Included);
}

static void PrintTodoItem(TodoItemDataInResponse todoItem, ICollection<DataInResponse>? included)
{
    // ...
}

Instead, the code for method PrintTodoItem needs to be duplicated, because the types are incompatible:

TodoItemPrimaryResponseDocument? getSingleResponse = await client.Api.TodoItems["1"].GetAsync();
PrintTodoItem1(getSingleResponse!.Data!, getSingleResponse.Included);

TodoItemCollectionResponseDocument? getMultiResponse = await client.Api.TodoItems.GetAsync();
foreach (TodoItemDataInResponse todoItem in getMultiResponse!.Data!)
{
    PrintTodoItem2(todoItem, getMultiResponse.Included);
}

static void PrintTodoItem1(TodoItems todoItem, ICollection<DataInResponse>? included)
{
    // ...
}

static void PrintTodoItem2(TodoItemDataInResponse todoItem, ICollection<DataInResponse>? included)
{
    // ...
}

Additionally, because there are duplicate types, it's unclear for consumers of the API what to upcast/type-check for when looping over the entries in included.

When using NSwag to generate the client, types appear as expected, which makes me believe the OAS is correct.

Expand to view the full OAS file

{
  "openapi": "3.0.1",
  "info": {
    "title": "JsonApiDotNetCoreExample",
    "version": "1.0"
  },
  "servers": [
    {
      "url": "https://localhost:44340"
    }
  ],
  "paths": {
    "/api/todoItems": {
      "get": {
        "tags": [
          "todoItems"
        ],
        "summary": "Retrieves a collection of todoItems.",
        "operationId": "getTodoItemCollection",
        "parameters": [
          {
            "name": "query",
            "in": "query",
            "description": "For syntax, see the documentation for the [`include`](https://www.jsonapi.net/usage/reading/including-relationships.html)/[`filter`](https://www.jsonapi.net/usage/reading/filtering.html)/[`sort`](https://www.jsonapi.net/usage/reading/sorting.html)/[`page`](https://www.jsonapi.net/usage/reading/pagination.html)/[`fields`](https://www.jsonapi.net/usage/reading/sparse-fieldset-selection.html) query string parameters.",
            "schema": {
              "type": "object",
              "additionalProperties": {
                "type": "string",
                "nullable": true
              },
              "example": ""
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Successfully returns the found todoItems, or an empty array if none were found.",
            "content": {
              "application/vnd.api+json": {
                "schema": {
                  "$ref": "#/components/schemas/todoItemCollectionResponseDocument"
                }
              }
            }
          },
          "400": {
            "description": "The query string is invalid."
          }
        }
      }
    },
    "/api/todoItems/{id}": {
      "get": {
        "tags": [
          "todoItems"
        ],
        "summary": "Retrieves an individual todoItem by its identifier.",
        "operationId": "getTodoItem",
        "parameters": [
          {
            "name": "id",
            "in": "path",
            "description": "The identifier of the todoItem to retrieve.",
            "required": true,
            "schema": {
              "type": "string"
            }
          },
          {
            "name": "query",
            "in": "query",
            "description": "For syntax, see the documentation for the [`include`](https://www.jsonapi.net/usage/reading/including-relationships.html)/[`filter`](https://www.jsonapi.net/usage/reading/filtering.html)/[`sort`](https://www.jsonapi.net/usage/reading/sorting.html)/[`page`](https://www.jsonapi.net/usage/reading/pagination.html)/[`fields`](https://www.jsonapi.net/usage/reading/sparse-fieldset-selection.html) query string parameters.",
            "schema": {
              "type": "object",
              "additionalProperties": {
                "type": "string",
                "nullable": true
              },
              "example": ""
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Successfully returns the found todoItem.",
            "content": {
              "application/vnd.api+json": {
                "schema": {
                  "$ref": "#/components/schemas/todoItemPrimaryResponseDocument"
                }
              }
            }
          },
          "400": {
            "description": "The query string is invalid."
          },
          "404": {
            "description": "The todoItem does not exist."
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "dataInResponse": {
        "required": [
          "id",
          "type"
        ],
        "type": "object",
        "properties": {
          "type": {
            "minLength": 1,
            "type": "string"
          },
          "id": {
            "minLength": 1,
            "type": "string"
          }
        },
        "additionalProperties": false,
        "discriminator": {
          "propertyName": "type",
          "mapping": {
            "tags": "#/components/schemas/tagDataInResponse",
            "todoItems": "#/components/schemas/todoItemDataInResponse"
          }
        },
        "x-abstract": true
      },
      "tagAttributesInResponse": {
        "type": "object",
        "properties": {
          "name": {
            "minLength": 1,
            "type": "string"
          }
        },
        "additionalProperties": false
      },
      "tagDataInResponse": {
        "allOf": [
          {
            "$ref": "#/components/schemas/dataInResponse"
          },
          {
            "type": "object",
            "properties": {
              "attributes": {
                "allOf": [
                  {
                    "$ref": "#/components/schemas/tagAttributesInResponse"
                  }
                ]
              },
              "relationships": {
                "allOf": [
                  {
                    "$ref": "#/components/schemas/tagRelationshipsInResponse"
                  }
                ]
              }
            },
            "additionalProperties": false
          }
        ],
        "additionalProperties": false
      },
      "tagIdentifier": {
        "required": [
          "id",
          "type"
        ],
        "type": "object",
        "properties": {
          "type": {
            "$ref": "#/components/schemas/tagResourceType"
          },
          "id": {
            "minLength": 1,
            "type": "string"
          }
        },
        "additionalProperties": false
      },
      "tagRelationshipsInResponse": {
        "type": "object",
        "properties": {
          "todoItems": {
            "allOf": [
              {
                "$ref": "#/components/schemas/toManyTodoItemInResponse"
              }
            ]
          }
        },
        "additionalProperties": false
      },
      "tagResourceType": {
        "enum": [
          "tags"
        ],
        "type": "string",
        "additionalProperties": false
      },
      "toManyTagInResponse": {
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/tagIdentifier"
            }
          }
        },
        "additionalProperties": false
      },
      "toManyTodoItemInResponse": {
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/todoItemIdentifier"
            }
          }
        },
        "additionalProperties": false
      },
      "todoItemAttributesInResponse": {
        "type": "object",
        "properties": {
          "description": {
            "type": "string"
          }
        },
        "additionalProperties": false
      },
      "todoItemCollectionResponseDocument": {
        "required": [
          "data"
        ],
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/todoItemDataInResponse"
            }
          },
          "included": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/dataInResponse"
            }
          }
        },
        "additionalProperties": false
      },
      "todoItemDataInResponse": {
        "allOf": [
          {
            "$ref": "#/components/schemas/dataInResponse"
          },
          {
            "type": "object",
            "properties": {
              "attributes": {
                "allOf": [
                  {
                    "$ref": "#/components/schemas/todoItemAttributesInResponse"
                  }
                ]
              },
              "relationships": {
                "allOf": [
                  {
                    "$ref": "#/components/schemas/todoItemRelationshipsInResponse"
                  }
                ]
              }
            },
            "additionalProperties": false
          }
        ],
        "additionalProperties": false
      },
      "todoItemIdentifier": {
        "required": [
          "id",
          "type"
        ],
        "type": "object",
        "properties": {
          "type": {
            "$ref": "#/components/schemas/todoItemResourceType"
          },
          "id": {
            "minLength": 1,
            "type": "string"
          }
        },
        "additionalProperties": false
      },
      "todoItemPrimaryResponseDocument": {
        "required": [
          "data"
        ],
        "type": "object",
        "properties": {
          "data": {
            "allOf": [
              {
                "$ref": "#/components/schemas/todoItemDataInResponse"
              }
            ]
          },
          "included": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/dataInResponse"
            }
          }
        },
        "additionalProperties": false
      },
      "todoItemRelationshipsInResponse": {
        "type": "object",
        "properties": {
          "tags": {
            "allOf": [
              {
                "$ref": "#/components/schemas/toManyTagInResponse"
              }
            ]
          }
        },
        "additionalProperties": false
      },
      "todoItemResourceType": {
        "enum": [
          "todoItems"
        ],
        "type": "string",
        "additionalProperties": false
      }
    }
  }
}

I'm using the next command to generate the client code:

dotnet kiota generate --language CSharp --class-name ApiClient --namespace-name GeneratedClient --output ./GeneratedClient --clean-output --clear-cache --openapi ..\JsonApiDotNetCoreExample\GeneratedSwagger\JsonApiDotNetCoreExample.json

Used versions:

• .NET 8 SDK v8.0.201 on Windows 11 23H2
• microsoft.openapi.kiota global tool v1.11.1 (latest available)
• Latest available NuGet package versions, as of today:

  <PackageReference Include="Microsoft.Kiota.Abstractions" Version="1.7.9" />
  <PackageReference Include="Microsoft.Kiota.Http.HttpClientLibrary" Version="1.3.6" />
  <PackageReference Include="Microsoft.Kiota.Serialization.Form" Version="1.1.3" />
  <PackageReference Include="Microsoft.Kiota.Serialization.Json" Version="1.1.5" />
  <PackageReference Include="Microsoft.Kiota.Serialization.Multipart" Version="1.1.2" />
  <PackageReference Include="Microsoft.Kiota.Serialization.Text" Version="1.1.2" />
  

[andrueastman]

Thanks for raising this @bkoelman

I believe the issue is that second endpoint (paths./api/todoItems/{id}.get) uses an inline schema for its response type with allOf. As schema is declared inline, kiota will interpret this as a different type and generate the inline model.

https://learn.microsoft.com/en-us/openapi/kiota/models#components-versus-inline-models

As the allOf is only of one type, any chance you get a different result if you modify the description to directly reference the todoItemDataInResponse without the allOf?

[bkoelman]

Thanks for investigating. If I patch the OAS manually as you suggested, the problem goes away.

We're using Swashbuckle's UseAllOfToExtendReferenceSchemas because the OpenAPI 3.0 spec doesn't allow the use of nullable and description without it (see here). So we get this output as a result.

Shouldn't Kiota just treat a single-element allOf the same as what's inside it? I think I've seen Kiota do that in other places already.

[andrueastman]

Shouldn't Kiota just treat a single-element allOf the same as what's inside it? I think I've seen Kiota do that in other places already.

I believe, you are correct. It probably should.

To resolve this, I suspect need to check what happens around here when the model declarations are being created.

kiota/src/Kiota.Builder/KiotaBuilder.cs

Line 1824 in 8c4e39f

if (schema.IsReferencedSchema() && !string.IsNullOrEmpty(typeNameForInlineSchema))

@bkoelman Would by any chance be willing to submit a PR for a failing test in this scenario to help out. I think the test would look very similar to this one.

kiota/tests/Kiota.Builder.Tests/KiotaBuilderTests.cs

Line 489 in 8c4e39f

public async Task DoesNotIntroduceIntermediateTypesForMeaninglessProperties(string additionalInformation)

[bkoelman]

I wish there were more hours in a day. It's taken me weeks before finding time to create the minimal repro, which was needed to know if we were doing something wrong. I'd like to contribute, but don't expect to be able to anytime soon, unfortunately.