Relationship update request may query read-only replica

[bart-degreed]

This bug affects APIs that use a master database to write changes to while using a set of read-only replicates to serve GET requests.

The query to determine initial state is sent to the read-only database on POST Many-to-many and DELETE To-many relationship requests.

Affected code:

JsonApiDotNetCore/src/JsonApiDotNetCore/Services/JsonApiResourceService.cs

Line 350 in 1b01e52

IReadOnlyCollection<TResource> leftResources = await _repositoryAccessor.GetAsync<TResource>(queryLayer, cancellationToken);

Instead it should call:

_repositoryAccessor.GetForUpdateAsync()

[bart-degreed]

This is not such a big problem after all, as all calls eventually reach GetAsync(), which is the place to override and switch databases based on IJsonApiRequest.IsReadOnly.