Basic feature parity with ActiveRecord

I should absolutely look at ActiveRecord to see the features they provide. The [basic overview page here](http://guides.rubyonrails.org/active_record_basics.html) already has some features that would be worth adding.

This issue can be closed once I have a list of the features I should add from AR.

Start with the linked Active Record Basics overview and compare its listed features with the current api-pls project. The issue does not name implementation files or tests; it is done when the relevant ActiveRecord features to add have been identified and documented as a list.

Written by the indexing model from the issue text.