# ActiveRecord Docs

- [`ActiveRecord::Migration` for methods used in migrations to change database structure](https://api.rubyonrails.org/classes/ActiveRecord/Migration.html)
- [`TableDefinition` object for adding columns and foreign keys](https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html#method-i-column)
- [`ActiveRecord::Peristence` methods](https://api.rubyonrails.org/classes/ActiveRecord/Persistence.html) for `save`, `update`, and `destroy`
- [`ActiveRecord::Associations::ClassMethods` (for `has_many` and `belongs_to`)](https://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html)
- [`ActiveRecord::QueryMethods` for the `where` method](https://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-where)
- [`ActiveRecord::Relation` for find_or_create_by](https://api.rubyonrails.org/classes/ActiveRecord/Relation.html#method-i-find_or_create_by)