[Critical] ASP.NET Core 9.0: AddOpenApi duplicates schema with a number suffix

[jaliyaudagedara]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I was migrating an ASP.NET Core Web API from .NET 8.0 to .NET 9.0.

As part of the migration, I was replacing AddSwaggerGen() with AddOpenApi() and seeing this critical issue. This basically inserts duplicated schema to OpenAPI specification. Solid OpenAPI specification is critical when integrating with services like APIM and hence subject is marked with Critical.

Consider the following minimal reproducible example.

csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.0" />
    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerUI" Version="7.2.0" />
  </ItemGroup>

</Project>

Startup.cs

namespace WebApplication3;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddOpenApi();
        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app)
    {
        app.UseSwaggerUI(x =>
        {
            x.SwaggerEndpoint("/openapi/v1.json", "My API");
        });

        app.UseHttpsRedirection();
        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapOpenApi();

            endpoints.MapControllers();
        });
    }
}

Program.cs

namespace WebApplication3;

public class Program
{
    public static void Main(string[] args)
    {
        IHost host = CreateHostBuilder(args).Build();
        host.Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
       Host.CreateDefaultBuilder(args)
           .ConfigureWebHostDefaults(webBuilder =>
           {
               webBuilder.UseStartup<Startup>();
           });
}

WeatherForecastController.cs

using Microsoft.AspNetCore.Mvc;

namespace WebApplication3.Controllers;

[ApiController]
[Route("/api/[controller]")]
public class WeatherForecastController : ControllerBase
{
    [HttpGet]
    public ActionResult<IEnumerable<WeatherForecast>> Get()
    {
        return Ok();
    }

    [HttpPost]
    public ActionResult<WeatherForecast> Create([FromBody] WeatherForecast weatherForecast)
    {
        return weatherForecast;
    }
}

Up to here, it's pretty standard.

Now carefully review the following WeatherForecast type.

namespace WebApplication3;

public class WeatherForecast
{
    public int Id { get; set; }

    public DateOnly Date { get; set; }

    public int TemperatureC { get; set; }

    public LocationDto Location { get; set; }
}

public class LocationDto
{
    public string Name { get; set; }

    public AddressDto Address { get; set; }
}

public class AddressDto
{
    string AddressLine { get; set; }

    // A circular reference, but not getting any errors
    public LocationDto RelatedLocation { get; set; }
}

When I run this:

Note the highlighted schema.

OpenAPI specification

{
    "openapi": "3.0.1",
    "info": {
        "title": "WebApplication3 | v1",
        "version": "1.0.0"
    },
    "servers": [
        {
            "url": "https://localhost:7286/"
        },
        {
            "url": "http://localhost:5013/"
        }
    ],
    "paths": {
        "/api/WeatherForecast": {
            "get": {
                "tags": [
                    "WeatherForecast"
                ],
                "responses": {
                    "200": {
                        "description": "OK",
                        "content": {
                            "text/plain": {
                                "schema": {
                                    "type": "array",
                                    "items": {
                                        "$ref": "#/components/schemas/WeatherForecast"
                                    }
                                }
                            },
                            "application/json": {
                                "schema": {
                                    "type": "array",
                                    "items": {
                                        "$ref": "#/components/schemas/WeatherForecast"
                                    }
                                }
                            },
                            "text/json": {
                                "schema": {
                                    "type": "array",
                                    "items": {
                                        "$ref": "#/components/schemas/WeatherForecast"
                                    }
                                }
                            }
                        }
                    }
                }
            },
            "post": {
                "tags": [
                    "WeatherForecast"
                ],
                "requestBody": {
                    "content": {
                        "application/json": {
                            "schema": {
                                "$ref": "#/components/schemas/WeatherForecast2"
                            }
                        },
                        "text/json": {
                            "schema": {
                                "$ref": "#/components/schemas/WeatherForecast2"
                            }
                        },
                        "application/*+json": {
                            "schema": {
                                "$ref": "#/components/schemas/WeatherForecast2"
                            }
                        }
                    },
                    "required": true
                },
                "responses": {
                    "200": {
                        "description": "OK",
                        "content": {
                            "text/plain": {
                                "schema": {
                                    "$ref": "#/components/schemas/WeatherForecast2"
                                }
                            },
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/WeatherForecast2"
                                }
                            },
                            "text/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/WeatherForecast2"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "AddressDto": {
                "type": "object",
                "properties": {
                    "relatedLocation": {
                        "$ref": "#/components/schemas/LocationDto2"
                    }
                }
            },
            "AddressDto2": {
                "type": "object",
                "properties": {
                    "relatedLocation": {
                        "$ref": "#/components/schemas/LocationDto4"
                    }
                }
            },
            "LocationDto": {
                "type": "object",
                "properties": {
                    "name": {
                        "type": "string"
                    },
                    "address": {
                        "$ref": "#/components/schemas/AddressDto"
                    }
                }
            },
            "LocationDto2": {
                "type": "object",
                "properties": {
                    "name": {
                        "type": "string"
                    },
                    "address": {
                        "$ref": "#/components/schemas/#/items/properties/location/properties/address"
                    }
                }
            },
            "LocationDto3": {
                "type": "object",
                "properties": {
                    "name": {
                        "type": "string"
                    },
                    "address": {
                        "$ref": "#/components/schemas/AddressDto2"
                    }
                }
            },
            "LocationDto4": {
                "type": "object",
                "properties": {
                    "name": {
                        "type": "string"
                    },
                    "address": {
                        "$ref": "#/components/schemas/#/properties/location/properties/address"
                    }
                }
            },
            "WeatherForecast": {
                "type": "object",
                "properties": {
                    "id": {
                        "type": "integer",
                        "format": "int32"
                    },
                    "date": {
                        "type": "string",
                        "format": "date"
                    },
                    "temperatureC": {
                        "type": "integer",
                        "format": "int32"
                    },
                    "location": {
                        "$ref": "#/components/schemas/LocationDto"
                    }
                }
            },
            "WeatherForecast2": {
                "type": "object",
                "properties": {
                    "id": {
                        "type": "integer",
                        "format": "int32"
                    },
                    "date": {
                        "type": "string",
                        "format": "date"
                    },
                    "temperatureC": {
                        "type": "integer",
                        "format": "int32"
                    },
                    "location": {
                        "$ref": "#/components/schemas/LocationDto3"
                    }
                }
            }
        }
    },
    "tags": [
        {
            "name": "WeatherForecast"
        }
    ]
}

Expected Behavior

Under components.schemas, there should be only 3 schemas

• AddressDto
• LocationDto
• WeatherForecast

Steps To Reproduce

https://github.com/jaliyaudagedara/aspnetcore-minimal-repros/tree/main/openapi-dup-schemas

Exceptions (if any)

N/A

.NET Version

9.0.200-preview.0.24575.35

Anything else?

N/A

[martincostello]

Please provide the repro as a GitHub repository, not a ZIP file.

[jaliyaudagedara]

sure, will do within next 30 min

[jaliyaudagedara]

@martincostello:
https://github.com/jaliyaudagedara/repro-aspnetcore-openapi-dup-schemas

Updated the original issue with the link as well.

[jaliyaudagedara]

Issue seems to be here:

aspnetcore/src/OpenApi/src/Services/Schemas/OpenApiSchemaStore.cs

Line 154 in af22eff

private void AddOrUpdateSchemaByReference(OpenApiSchema schema, string? baseTypeSchemaId = null, bool captureSchemaByRef = false)

{
    "type": "array",
    "items": {
        "type": "object",
        "properties": {
            "location": {
                "type": "object",
                "properties": {
                    "address": {
                        "type": "object",
                        "properties": {
                            "relatedLocation": {
                                "type": "object",
                                "properties": {
                                    "address": {
                                        "$ref": "#/items/properties/location/properties/address",
                                        "x-schema-id": "AddressDto"
                                    }
                                },
                                "x-schema-id": "LocationDto"
                            }
                        },
                        "x-schema-id": "AddressDto"
                    }
                },
                "x-schema-id": "LocationDto"
            }
        },
        "x-schema-id": "WeatherForecast"
    }
}

LocationDto schema is different.

{
    "type": "object",
    "properties": {
        "address": {
            "$ref": "#/items/properties/location/properties/address",
            "x-schema-id": "AddressDto"
        }
    },
    "x-schema-id": "LocationDto"
}

{
    "type": "object",
    "properties": {
        "address": {
            "type": "object",
            "properties": {
                "relatedLocation": {
                    "type": "object",
                    "properties": {
                        "address": {
                            "$ref": "#/items/properties/location/properties/address",
                            "x-schema-id": "AddressDto"
                        }
                    },
                    "x-schema-id": "LocationDto"
                }
            },
            "x-schema-id": "AddressDto"
        }
    },
    "x-schema-id": "LocationDto"
}

Should the OpenApiSchema for WeatherForecast be this,

{
    "type": "object",
    "properties": {
        "location": {
            "type": "object",
            "properties": {
                "address": {
                    "type": "object",
                    "properties": {
                        "relatedLocation": {
                            "type": "object",
                            "properties": {
                                "address": {
                                    "$ref": "#/items/properties/location/properties/address",
                                    "x-schema-id": "AddressDto"
                                }
                            },
                            // added
                            "$ref": "#/items/properties/location",
                            "x-schema-id": "LocationDto"
                        }
                    },
                    "x-schema-id": "AddressDto"
                }
            },
            "x-schema-id": "LocationDto"
        }
    },
    "x-schema-id": "WeatherForecast"
}

[jaliyaudagedara]

Updated the repro with minimal APIs,

WebApplicationBuilder builder = WebApplication.CreateBuilder(args);

// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
builder.Services.AddOpenApi();

WebApplication app = builder.Build();

app.MapOpenApi();
app.UseSwaggerUI(x =>
{
    x.SwaggerEndpoint("/openapi/v1.json", "My API");
});

app.UseHttpsRedirection();

app.MapGet("/weatherforecast", () =>
{
    return Enumerable.Empty<WeatherForecast>();
})
.Produces<IEnumerable<WeatherForecast>>()
.WithName("GetWeatherForecasts");

app.MapPost("/weatherforecast", (WeatherForecast weatherForecast) =>
{
    return weatherForecast;
})
.Produces<WeatherForecast>()
.WithName("CreateWeatherForecast");

app.Run();

public class WeatherForecast
{
    public LocationDto Location { get; set; }
}

public class LocationDto
{
    public AddressDto Address { get; set; }
}

public class AddressDto
{
    public LocationDto RelatedLocation { get; set; }
}

[jankaltenecker]

Duplicate issue: #58968

[akamor]

@martincostello Lots of additional reproductions and information in the issue @jankaltenecker just linked. It really looks like openapi is dead on arrival in dotnet9. It cannot even support quite trivial schemas given this duplication issue.

[jaliyaudagedara]

@jankaltenecker, thanks for linking the issue.

@akamor, completely agree.

[captainsafia]

Closing in favor of #58968.

See update at #58968 (comment).