ActiveRecord Repository

This is an implementation of the repository pattern for ActiveRecord. Using this allows splitting the domain model and persistence classes.

WARNING: This is currently merely a proof of concept. This means that testing and refactoring have often been put on the back burner.

TODO

Loading
- Loading relations
  - Avoiding N+1 queries
Saving
- Saving relations
Keep a registry of the repository classes
- Indexed by the classes they map to
- Use this to find repository class for relations
  - Caveat: What if there are 2 repositories for a relation we're looking for?
    - Need a way to specify that somewhere
      - In the repository is the only place that makes sense
Probably need to restrict other calls to Repository
- User::Repository.create
Entity#initialize and #update should basically be the same
- Maybe the only difference is that initialize will set things to nil
- They could use a lot of refactoring
Relations between entities
- belongs_to
- has_many
- has_one
- has_many through:
- Cascading deletions
Entity#changed?
Identity mapping
Use module builder pattern in ActiveModel.entity
- Add more options
Use module factory (and module builder) pattern in ActiveRecord.repository
- Add options
  - Setting entity class
  - Setting table_name
  - Setting a different primary key than id
  - Maybe define indexes
More validations