Open Api fails to generate correct schema type for some properties

[mattiasnordqvist]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

generates this schema

Expected Behavior

I would expect this schema

"D": {
  "required": [
    "b",
    "c"
  ],
  "type": "object",
  "properties": {
    "b": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/B"
      }
    },
    "c": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/B"
      }
    }
  }
}

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

9.0.4

Anything else?

No response

[NWessel]

When would a fix for this be a realistic expectation? I know you guys are busy

[simonlevinsson-spinit]

Just a FYI about the required part of the bug report. It is not connected to the issue as it's a global configuration set for the schema generator in the project.

[wuzzeb]

I also hit this problem and was able to make a small reproducible and runnable example. It is a single change 5a705dd on top of the default dotnet new webapi template. See https://github.com/wuzzeb/openapi-bug for the runnable example.

9.0.4 generates

"WeatherForecast": {
  "required": [
    "cities"
  ],
  "type": "object",
  "properties": {
    "date": {
      "type": "string",
      "format": "date"
    },
    "cities": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/City"
      }
    },
    "citiesMore": {
      "type": "array",
      "items": { },
      "nullable": true
    }
  }
}

Interestingly, if you switch it to 9.0.3, it instead generates

    "citiesMore": {
      "type": "array",
      "items": {
        "$ref": "#/components/schemas/#/properties/cities/items"
      },
      "nullable": true
    }

So it seems like nullability and duplication isn't an issue here since in both lists City is non-nullable so no need to duplicate. But maybe some of the nullability/duplication fixes between 9.0.3 and 9.0.4 broke this situation?

[p3rh5g]

I have made this schema transformer as a workaround until this is fixed:

public sealed class FixBrokenReferencesInArraysSchemaTransformer : IOpenApiSchemaTransformer
{
    public Task TransformAsync(
        OpenApiSchema schema,
        OpenApiSchemaTransformerContext context,
        CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(schema);

        if (schema.Properties is null)
        {
            return Task.CompletedTask;
        }

        var propertiesToFix = schema.Properties
            .Select(x => x.Value)
            .Where(x => x.Type == "array")
            .Where(x => x.Items is not null)
            .Where(x => !string.IsNullOrEmpty(x.Items.Reference?.Id))
            .Where(x => x.Items.Annotations is not null);

        foreach (var property in propertiesToFix)
        {
            if (!property.Items.Annotations.TryGetValue("x-schema-id", out var schemaId))
            {
                continue;
            }

            property.Items.Reference = new OpenApiReference
            {
                Type = ReferenceType.Schema,
                Id = schemaId.ToString(),
            };
        }

        return Task.CompletedTask;
    }
}

[mattiasnordqvist]

problem persists in 9.0.5