Load columns from schema to avoid AR ignored/only column configuration

[bensheldon]

Fixes #286

This PR recreates the Active Record logic for fetching the columns from the schema cache before they are filter based on Active Record's ignored_columns/only_columns configuration.

• columns is defined here: https://github.com/rails/rails/blob/5d4cfc3e73a77bd5ee4fba3ec42e8c3782c9ab02/activerecord/lib/active_record/model_schema.rb#L443-L450
• ...and populated here: https://github.com/rails/rails/blob/5d4cfc3e73a77bd5ee4fba3ec42e8c3782c9ab02/activerecord/lib/active_record/model_schema.rb#L609-L615

[drwl]

Hi @bensheldon apologies on the months long delay in response -- the issue was helpful in providing context. I do think that this could cause regressions for other users of this gem because adding this in its current state would mean ignored columns will appear in annotations.

Can this new behavior be gated behind an option flag with the default preserving the existing behavior?

[bensheldon]

Can this new behavior be gated behind an option flag with the default preserving the existing behavior?

Yep, let me give that a shot.

[bensheldon]

@drwl ok, ready to go. I'd love your feedback on the configuration value naming. load_columns_from_schema is how it works, I dunno if something declarative like include_active_record_ignored_columns would be better?

Also, I wasn't able to run all the test matrix locally so I'm not sure if I needed to change all the TestDefault model files.