In Microsoft.OData.Client 7.21.3 the Microsoft.OData.Client.DataService.Context.BulkUpdate() method appears to force the OData-Version header to 4.01 regardless of the
maxProtocolVersion provided to the DataServiceContext constructor. I am using Microsoft.AspNetCore.OData 8.2.5 on my server, and out of the box it cannot deal with this protocol of OData for bulk updates (Specifically the DeltaSet<T> parameter of my entity set patch action is always null). In Postman if I send an identical request as the client to the server but with the OData-Version header set to 4.0 the server handles this without issue. My questions are as follows:

• How do I send a bulk update request to an OData 4.0 server with Microsoft.OData.Client?
• Why does BulkUpdate() force the protocol version to 4.01?
• Is this an issue with my client or my server (i.e. do I need to direct this issue at Microsoft.AspNetCore.OData)?

I should also note that I am using OData Connected Service on my client for code generation, but I am not sure this is relevant.

Assemblies affected

• Microsoft.OData.Client 7.21.3
• Microsoft.AspNetCore.OData 8.2.5

Reproduce steps

I implemented Sample Request 1 from the OData Client Bulk Update Operations examples on my client.
And implemented an endpoint on my server to "patch a collection of entities" from this Microsoft.AspNetCore.OData tutorial.

Note: I modified the client example to work with the Shape, Circle, Rectangle models from the server example.

Client code:

Default.Container context = new Default.Container(new Uri("https://localhost:7092/odata/"), Microsoft.OData.Client.ODataProtocolVersion.V4);

Shape s1 = new Shape { Id = 1, Area = 10 };
context.AddToShapes(s1);

Shape s2 = new Shape { Id = 2, Area = 20 };
context.AddToShapes(s2);

context.BulkUpdate(s1, s2); // fails

Server code:

// Program.cs
var builder = WebApplication.CreateBuilder(args);
var modelBuilder = new ODataConventionModelBuilder();
modelBuilder.EntitySet<Shape>("Shapes");

builder.Services.AddControllers()
    .AddOData(opts =>
    {
        opts.EnableQueryFeatures().AddRouteComponents("odata", modelBuilder.GetEdmModel());
    });

// ShapesController.cs
public class ShapesController : ODataController
{
    private static List<Shape> shapes = new List<Shape>
    {
        new Rectangle { Id = 1, Length = 7, Width = 4, Area = 28 },
        new Circle { Id = 2, Radius = 3.5, Area = 38.5 },
        new Rectangle { Id = 3, Length = 8, Width = 5, Area = 40 }
    };

    public async Task<ActionResult> Patch([FromBody] DeltaSet<Shape> deltaSet)
    {
        if (deltaSet == null)
        {
            return BadRequest();
        }

        foreach (Delta<Shape> delta in deltaSet)
        {
            if (delta.TryGetPropertyValue("Id", out object idAsObject))
            {
                var shape = shapes.SingleOrDefault(d => d.Id.Equals(idAsObject));
                delta.Patch(shape);
            }
        }

        return Ok();
    }
}

Expected result

The BulkUpdate() method would succeed on the client, and the DeltaSet<T> parameter on the server would not be null when the action executes.

Actual result

The DeltaSet<T> parameter is null when the server action executes, meaning the server returns BadRequest and the client update operation fails.