[OpenAPI] Get parameter description with [FromQuery]

[martincostello]

Get parameter description with [FromQuery]

Get an OpenAPI description when attribute is on an object's property.

Description

Get the description from the associated object's property when [FromQuery] is applied to a property of an object used as a [FromQuery] parameter.

Fixes #61297

[martincostello]

This change is to make this assertion happy:

aspnetcore/src/OpenApi/src/Extensions/ApiDescriptionExtensions.cs

Line 44 in 02125bd

Debug.Assert(apiDescription.RelativePath != null, "Relative path cannot be null.");

[Copilot]

Pull Request Overview

This PR enhances OpenAPI parameter description extraction to support descriptions from properties with [FromQuery] attributes. When a parameter uses [FromQuery] on an object property, the OpenAPI generator will now extract the description from the property's [Description] attribute.

Key changes:

• Enhanced parameter description extraction logic to check model metadata for property-level descriptions
• Added comprehensive test coverage for both [AsParameters] and [FromQuery] scenarios
• Fixed a minor issue with route template handling in test infrastructure

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
OpenApiDocumentService.cs	Enhanced GetParameterDescriptionFromAttribute method to extract descriptions from property metadata when parameter-level descriptions are not available
OpenApiSchemaService.ParameterSchemas.cs	Added test cases for both [AsParameters] and [FromQuery] scenarios with description attributes, including test model definitions
OpenApiDocumentServiceTestsBase.cs	Fixed potential null reference issue in route template handling for test infrastructure

Comments suppressed due to low confidence (1)

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs:534

• The test creates an action descriptor but doesn't have an 'Act' section. The test should explicitly invoke the OpenAPI generation process to ensure the parameter description extraction is being tested properly.

        var actionDescriptor = CreateActionDescriptor(nameof(TestFromQueryController.GetWithFromQueryDto), typeof(TestFromQueryController));

[martincostello]

I'm not 100% sure this is right, as it feels wrong to depend on a specific model metadata implementation, but I couldn't immediately see an obvious interface-y/abstract way to query the same information and this was "right there" in the debugger.

[captainsafia]

I think for practical cases this is sufficient.

The APIs will only ever end up consuming two metadata types:

• EndpointModelMetadata which is used for minimal API
• DefaultModelMetadata for MVC

The minimal API cases end up getting handled by the IParameterInfoParameterDescriptor because of the way we map everything, including [AsParameters] to parameter descriptions via things like PropertyAsParameterInfo.

This is also why the bug reports that we've received specifically site this gap in controllers and not minimal APIs.

So although it looks werid and is awakward, I think this is the correct way give the fact that MVC relies on model metadata and minimal API doesn't.