Create an :active_record_connection_adapters load hook which is run a…

…fter ActiveRecord::ConnectionAdapters is defined.

Since callbacks defined with :active_record my establish a connection (such as "active_record.initialize_database" in the active record railtie) it can create order dependence since the adapters need to be registered first or else establishing a connection will raise an exception. So, let's define a new load hook that can be used for registering adapters, and run it as soon as ActiveRecord::ConnectionAdapters is defined, before the :active_record hooks are run.

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Create an `active_record_connection_adapters` load hook which is run after
+    `ActiveRecord::ConnectionAdapters` is defined. It can be used to register custom
+    connection adapters.
+
+    *Andrew Novoselac*
+
 *   `DatabaseConfigurations#configs_for` can accept a symbol in the `name` parameter.
 
     *Andrew Novoselac*

activerecord/lib/active_record/connection_adapters.rb

@@ -69,6 +69,8 @@ def resolve(adapter_name) # :nodoc:
     register "trilogy", "ActiveRecord::ConnectionAdapters::TrilogyAdapter", "active_record/connection_adapters/trilogy_adapter"
     register "postgresql", "ActiveRecord::ConnectionAdapters::PostgreSQLAdapter", "active_record/connection_adapters/postgresql_adapter"
 
+    ActiveSupport.run_load_hooks(:active_record_connection_adapters)
+
     eager_autoload do
       autoload :AbstractAdapter
     end

guides/source/engines.md

@@ -1486,6 +1486,7 @@ These are the load hooks you can use in your own code. To hook into the initiali
 | `ActiveModel::Model`                 | `active_model`                       |
 | `ActiveRecord::Base`                 | `active_record`                      |
 | `ActiveRecord::TestFixtures`         | `active_record_fixtures`             |
+| `ActiveRecord::ConnectionAdapters`   | `active_record_connection_adapters`  |
 | `ActiveRecord::ConnectionAdapters::PostgreSQLAdapter`    | `active_record_postgresqladapter`    |
 | `ActiveRecord::ConnectionAdapters::Mysql2Adapter`        | `active_record_mysql2adapter`        |
 | `ActiveRecord::ConnectionAdapters::TrilogyAdapter`       | `active_record_trilogyadapter`       |