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+* Add basic API for connection switching to support multiple databases.
+
+ 1) Adds a `connects_to` method for models to connect to multiple databases. Example:
+
+ ```
+ class AnimalsModel < ApplicationRecord
+ self.abstract_class = true
+
+ connects_to database: { writing: :animals_primary, reading: :animals_replica }
+ end
+
+ class Dog < AnimalsModel
+ # connected to both the animals_primary db for writing and the animals_replica for reading
+ end
+ ```
+
+ 2) Adds a `connected_to` block method for switching connection roles or connecting to
+ a database that the model didn't connect to. Connecting to the database in this block is
+ useful when you have another defined connection, for example `slow_replica` that you don't
+ want to connect to by default but need in the console, or a specific code block.
+
+ ```
+ ActiveRecord::Base.connected_to(role: :reading) do
+ Dog.first # finds dog from replica connected to AnimalsBase
+ Book.first # doesn't have a reading connection, will raise an error
+ end
+ ```
+
+ ```
+ ActiveRecord::Base.connected_to(database: :slow_replica) do
+ SlowReplicaModel.first # if the db config has a slow_replica configuration this will be used to do the lookup, otherwise this will throw an exception
+ end
+ ```
+
+ *Eileen M. Uchitelle*
+
* Enum raises on invalid definition values
When defining a Hash enum it can be easy to use [] instead of {}. This