Feature request: support resources with injected DbContext

[bart-degreed]

Description

Getting a resource by ID with sparse fieldsets fails when that resource has a constructor to inject the DbContext, as described here: https://docs.microsoft.com/en-us/ef/core/modeling/constructors.

Example:

public sealed class User : Identifiable
{
    public User(AppDbContext context)
    {
    }
}

This fails because IQueryableExtensions.CallGenericSelectMethod (and a few other places) assumes the entity has a parameterless constructor, causing an exception to be thrown at the statement:

Expression.New(sourceType)

Environment

latest master branch

[bart-degreed]

This also fails when trying to delete a resource, due to the usage of:

Activator.CreateInstance(typeof(TResource))

in DefaultResourceService.

[maurei]

That's an interesting feature of EF Core feature that I hadn't seen yet. I think it would be important to investigate if assuming parameterless constructors will or will not lead to JADNC being more tightly coupled with EF Core, because I feel such "EF Core parameter injection" is very EF-specific. But at the same time, having constructors with parameters in general to set read-only properties for models is not necessarily EF-Core specific, so it might/should be OK.

Either way I don't expect I will be able to work on this in the near future as I am currently low on development resources for JADNC (which is why I've been late in replying to your latest issues, my apologies for that)