Cannot write a nested delta payload to a top-level resource

[mikepizzo]

A valid response to PATCH against a single resource with a collection is a response containing a nested delta resource set. However, ODL doesn't allow you to write a top-level resource with a nested DeltaResourceSet.

Assemblies affected

OData.Net 7.x

Reproduce steps

1. Create a resource writer
2. Call WriteStart(resource)
3. Call WriteStart(nestedResourceInfo)
4. Call WriteStart(deltaResourceSet)

Expected result

Successfully write the resource with the nested resource set as an nested delta collection.

Actual result

An error, since you can't write a delta resource set if you start with a resource writer.

Additional detail

Today that is not possible because you can only write a delta response if you declare in your top-level resource set writer that you are writing a delta payload.

There is no longer any reason to declare up-front whether a writer is writing a delta request/response versus a non-delta request/response. A user should be able to call WriteStartDeltaResourceSet and write a delta resource set at the top level or nested within a resource.