Support for eager loading specific columns without requiring those columns

[samatcd]

When eager loading specific columns on a related record, you can use a special syntax to define the columns per the Laravel docs:

$books = App\Models\Book::with('author:id,name')->get();

When using a standard Laravel relationship definition, you don't need to specify the key fields in this eager loading, but you do when using a composite relationship. E.g., let's say I have the following relationship:

$this->hasOne(Author::class, ['author_id', 'ghostwriter_id'], ['author_id', 'ghostwriter_id']);

In order for the eager loading to work properly, I need to specify the key fields in the eager loading (even though I don't need those values).

$books = App\Models\Book::with('author:id,name,author_id,ghostwriter_id')->get();

It would be nice if those could be automatically handled without having to include them.