OpenApi throws InvalidOperationException: JsonPropertyInfo

[louislewis2]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

After updating a code base, I noticed the following scenario throws an exception on OpenApi generation.
The api endpoint still works as expected, so this only seems to break the generation of the json document.

Please see the further details below.

Expected Behavior

Expect to see the json returned.

Steps To Reproduce

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

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.8" />
  </ItemGroup>

</Project>

namespace WebApplication1
{
    using System.ComponentModel.DataAnnotations;

    public class Person
    {
        public Person(string name)
        {
            Name = name;
        }

        [Required]
        public string Name { get; }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.

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

            var app = builder.Build();

            // Configure the HTTP request pipeline.
            if (app.Environment.IsDevelopment())
            {
                app.MapOpenApi();
            }

            app.MapPost("/person", (Person p) => { });

            app.UseHttpsRedirection();

            app.MapControllers();

            app.Run();
        }
    }
}

The above code results in the exception when hitting the "/openapi/v1.json" endpoint

Removing the [Required] attribute on the Name property removes the exception on document generation, but of course is not what is desired.

Exceptions (if any)

System.InvalidOperationException: JsonPropertyInfo 'name' defined in type 'WebApplication1.Person' is marked required but does not specify a setter.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_JsonPropertyRequiredAndNotDeserializable(JsonPropertyInfo jsonPropertyInfo)
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo.Configure()
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.ConfigureProperties()
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.Configure()
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.<EnsureConfigured>g__ConfigureSynchronized|172_0()
   at System.Text.Json.JsonSerializerOptions.GetTypeInfoInternal(Type type, Boolean ensureConfigured, Nullable`1 ensureNotNull, Boolean resolveIfMutable, Boolean fallBackToNearestAncestorType)
   at System.Text.Json.Schema.JsonSchemaExporter.GetJsonSchemaAsNode(JsonSerializerOptions options, Type type, JsonSchemaExporterOptions exporterOptions)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaService.CreateSchema(OpenApiSchemaKey key)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaStore.GetOrAdd(OpenApiSchemaKey key, Func`2 valueFactory)
   at Microsoft.AspNetCore.OpenApi.OpenApiSchemaService.GetOrCreateSchemaAsync(Type type, IServiceProvider scopedServiceProvider, IOpenApiSchemaTransformer[] schemaTransformers, ApiParameterDescription parameterDescription, Boolean captureSchemaByRef, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetJsonRequestBody(IList`1 supportedRequestFormats, ApiParameterDescription bodyParameter, IServiceProvider scopedServiceProvider, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetRequestBodyAsync(ApiDescription description, IServiceProvider scopedServiceProvider, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOperationAsync(ApiDescription description, HashSet`1 capturedTags, IServiceProvider scopedServiceProvider, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOperationsAsync(IGrouping`2 descriptions, HashSet`1 capturedTags, IServiceProvider scopedServiceProvider, IOpenApiOperationTransformer[] operationTransformers, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiPathsAsync(HashSet`1 capturedTags, IServiceProvider scopedServiceProvider, IOpenApiOperationTransformer[] operationTransformers, IOpenApiSchemaTransformer[] schemaTransformers, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.OpenApi.OpenApiDocumentService.GetOpenApiDocumentAsync(IServiceProvider scopedServiceProvider, HttpRequest httpRequest, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Builder.OpenApiEndpointRouteBuilderExtensions.<>c__DisplayClass0_0.<<MapOpenApi>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F56B68D2B55B5B7B373BA2E4796D897848BC0F04A969B1AF6260183E8B9E0BAF2__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass2_0.<<MapGet0>g__RequestHandler|5>d.MoveNext()

.NET Version

Host: 9.0.8 SDK: 9.0.304 [C:\Program Files\dotnet\sdk]

Anything else?

No response

[martincostello]

This looks like a requirement of System.Text.Json (which is in the dotnet/runtime repo with regards to any issues).

The fix is to add a setter:

- [Required]
- public string Name { get; }
+ public string Name { get; set; }

If haven't tried it, but you may be able to make it internal if you don't wish it to be public.

Alternatively, I haven't tried this, but you could change to the following syntax if you want to enforce it is set by the compiler:

public class Person
{
-   public Person(string name)
-   {
-       Name = name;
-   }

    [Required]
-   public string Name { get; }
+   public required string Name { get; init; }
}

After updating a code base

From what?

[louislewis2]

Hi @martincostello

I understand that adding the init keyword could fix this.
However this pattern exists in code bases spanning over 10 years.
So it is not as simple as adding the keyword.

This used to just work.

As I mentioned the model binding still works, so the endpoint whether minimal or controller still works as expected.
This only breaks on the OpenApi document generation.

The update I am referring too, is removing the previous Swagger based document generation to the new MapOpenApi() generation.

[louislewis2]

This repository https://github.com/louislewis2/OpenApiBug
contains code which will show the bug, it also shows the endpoint still work and the only issue is the document generation.

[louislewis2]

[louislewis2]

I hope the above added details, helps to show the request part of Asp.Net works as expected.
The only issue, is the "new" OpenApi implementation from Microsoft.AspNetCore.OpenApi.

[martincostello]

This used to just work.

Whilst true, this is a bit comparing oranges and apples.

Swashbuckle.AspNetCore and Microsoft.AspNetCore.OpenApi are completely different implementations of OpenAPI document generation.

The former uses reflection to build the document (and depending how you configure it, can use Newtonsoft.Json), where as the latter builds on top of System.Text.Json's JSON schema functionality, which has its own opinions and requirements, and because System.Text.Json has a source generator, allows Microsoft.AspNetCore.OpenApi to be native AoT compatible.

I don't think this is a bug as far as ASP.NET Core is concerned, it's a design consequence of the use of System.Text.Json.

If the code as given should work as-is with the JSON schema functionality, then this is an issue for System.Text.Json in the dotnet/runtime repository.

From doing a quick search, it looks like there's already an issue open around this: dotnet/runtime#78098

As I mentioned the model binding still works, so the endpoint whether minimal or controller still works as expected.

I think you don't see the problem there because they go down different code paths and/or use reflection for deserialization (as your repro doesn't appear to be using native AoT and/or source generators).

[danmoseley]

Closing as answered. Thanks @martincostello

[SicJG]

@louislewis2
consider following workaround

public class Person
{
    [System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
    public Person(string name)
    {
        Name = name;
    }

    [System.Text.Json.Serialization.JsonConstructor]
    private Person(){}

    [Required]
    public required string Name { get; init;}
}