Allows two models to use the same table but have different primary keys.

Move delegation reponsibilities of Relation to a module. Also precompile method missing calls for rofscale.

Clean up the cache before the request in case we are running in the reload_classes_only_on_change schema.

Allow nested attributes in associations to update values in it's owner object.  Fixes a regression from 3.0.x

With transactional fixtures enabled, the session records would end up in
@_current_transaction_records, and at the end of the transaction,
methods would be called on them that would trigger method_missing and
trigger attribute methods to be generated.

However, at this point the sessions table would not exist, and the
columns were not cached, so an exception would be raised because we
can't find the columns to generate attribute methods for.

Not sure exactly why this didn't crop up before but there have been
changes to the schema cache code and perhaps that means that column data
that was cached previously at that point is now uncached.

It was a bad idea to rescue exceptions here. This can interfere with
transaction rollbacks which seems to be the cause of current CI
failure.

Instead, each adapter should implement its own DB-specific O(1)
implementation, and we fall back on the generic, slower, implementation
otherwise.

This can be turned off by setting `config.reload_classes_only_on_change` to false.

Extensions like Active Record should add their respective files like db/schema.rb and db/structure.sql to `config.watchable_files` if they want their changes to affect classes reloading.

Thanks to https://github.com/paneq/active_reload and Pastorino for the inspiration. <3

Add ActiveSupport::Cache::NullStore to expose caching interface without actually caching for development and test environments.

because with select p.* you can no longer use count(). Using count will result in an SQL error message.

people.* will not work when the alias is named p