c# - Swagger EF Core 3.1 Delta<Object> Request Body - Show Object Schema not Odata.Delta

Question

I've recently started using Swagger/Swashbuckle in my EF Core project.

When I've added a Patch API to the documentation the Request Body's Example value / Schema is showing details for the Delta not my object. Since it is a subset of the object's properties that need to be posted, is there a way to show my objects schema?

What swagger is showing

What I'd like (screen shot is from the Post API call)

The swagger and API's signature are below.

/// <summary>
/// Updates the provided Absence Reason.
/// </summary>
/// <remarks>
/// Runs bespoke Patch/Validation logic.
/// Updates the Absence Reason then returns the record.
/// </remarks>
/// <param name="key" required="true">Id of the Absence Reason being updated.</param>
/// <param name="delta" required="true">A delta of the updated Absence Reason record.</param>
/// <returns>Returns the created Absence Reason</returns>
/// <response code="204">Returns the updated Absence Reason.</response>
/// <response code="400">Invalid Absence Reason Record, Missing Row Version etc.</response>
/// <response code="404">Absence Reason not found.</response>
/// <response code="412">Record has been updated since the version provided.</response>
[ApiExplorerSettings]
[HttpPatch("odata/[controller]({key})")]
[Produces("application/json")]
[ProducesResponseType(typeof(AbsenceReason), StatusCodes.Status204NoContent)]
[ProducesResponseType(400)]
[ProducesResponseType(404)]
[ProducesResponseType(412)]
[Authorize(Policy = AuthPolicyNames.GOIAdminRole)]
public IActionResult Patch([FromODataUri] long key, Delta<AbsenceReason> delta)

Edit to add additional information in response to AlFranco

Screen shot of Watch on Reference

The _assemblyName from your code is "Microsoft.AspNetCore.OData, Version=7.4.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"

The trimmed down XML file created by VS documentation is:

        <member name="M:ESRGOI.Controllers.AbsenceReasonsController.Patch(System.Int64,Microsoft.AspNet.OData.Delta{ESRGOI.Models.AbsenceReason})">
            <summary>
            Updates the provided Absence Reason.
            </summary>
            <param name="key" required="true">Id of the Absence Reason being updated.</param>
            <param name="delta" required="true">A delta of the updated Absence Reason record.</param>
        </member>

Edit 2 Ok, I've managed to come up with a solution based on AlFranco's response.

It should be noted in the Swagger my models don't include the namespace. I originally tried including the namespace but received the below error: /components/schemas/ESRGOI.Models.AbsenceReason does not exist in document

public class DeltaOperationFilter : IOperationFilter
{
  private const string _deltaParam = "Delta";

  public void Apply(OpenApiOperation operation, OperationFilterContext context)
  {
    if (operation.RequestBody == null) return;

    var deltaTypes =
        operation.RequestBody
            .Content
            .Where(x => x.Value.Schema.Reference.Id.EndsWith(_deltaParam));

    foreach (var (_, value) in deltaTypes)
    {
      var schema = value.Schema;
      string model = schema.Reference.Id.Substring(0, schema.Reference.Id.Length - _deltaParam.Length);
      schema.Reference.Id = model;
    }
  }
}

Answer 1

Ok, so to do this you need to create an IOperationFilter

This worked for me:

    public class DeltaOperationFilter : IOperationFilter
    {
        private const string DeltaWrapper = "Microsoft.AspNet.OData.Delta`1";
        private readonly string _assemblyName = typeof(Microsoft.AspNet.OData.Delta).Assembly.FullName;

        public void Apply(OpenApiOperation operation, OperationFilterContext context)
        {                                                               
            if (operation.RequestBody == null) return;
            
            var deltaTypes =
                operation.RequestBody
                    .Content
                    .Where(x => x.Value.Schema.Reference.Id.StartsWith(DeltaWrapper));

            foreach (var (_, value) in deltaTypes)
            {
                var schema = value.Schema;
                var deltaType = Type.GetType(schema.Reference.Id+ ", " + _assemblyName);
                var deltaArgument = deltaType?.GetGenericArguments().First();
                schema.Reference.Id = deltaArgument?.FullName ?? schema.Reference.Id;
            }
        }
    }

The only thing you need to do afterwards is to register in swaggergen

// Assuming you are in Startup.cs ConfigureServices
services.AddSwaggerGen(c => c.OperationFilter<DeltaOperationFilter>());

By the way, are you able to use the Delta<T> apply properly on your entities? I'm going to use patch with some endpoints but would like to use Delta<DTO> and then transform it and apply it to Delta<Entity> that will actually persists. I'm particularly interested in the approach you'd be taking :)

Thanks!