A multi-database connection scheme for Rails 3, supporting testing and migrations
Easy to use
Bundle the gem
Define a second set of databases in your database.yml file. Use a prefix to differentiate from the core database.
Add “use_db :prefix => 'your_other_database_prefix_” to the Model
gem “use_db”, “~> 0.1.4”
Rails 3.1 -> 4.1
gem “use_db”, “~> 0.2.0”
gem “use_db”, “~> 0.3.0”
Insert a reference to use_db in your model, with a :prefix and/or :suffix
class MyModel < ActiveRecord::Base use_db :prefix => "your_other_database_prefix_", :suffix => "_is_legacy" end
This maps to a database in database.yml named:
So this is what your database.yml should look like:
your_other_database_prefix_test_is_legacy adapter: mysql database: other_test_db ... your_other_database_prefix_development_is_legacy adapter: mysql database: other_dev_db ...
You may find it useful (and more DRY) to define an abstract model to inherit from to avoid littering use_db in multiple places:
class LegacyDataBase < ActiveRecord::Base use_db :prefix => "your_other_database_prefix_", :suffix => "_is_legacy" self.abstract_class = true end class MyModel < LegacyDataBase end
Each migration intended for a different database needs to be told which to use. Do this by adding a method “self.database_model” and returning the class name which defines the other database. If you don't, it defaults to the core database like normal.
class ChangeOtherDatabaseTable < ActiveRecord::Migration # For clarity leave me at the top of the class. def self.database_model # Examples depending if you're using an abstract class or not: # return "LegacyDataBase" # return "MyModel" end end
In order to test multiple databases, you must require the test setup class and invoke a task which clones the development database structure and copies it into the test database, clearing out the existing test data. There is a single helper method which executes this task and you invoke it as follows:
require 'use_db_test_setup' UseDbTestSetup.prepare_test_db(:prefix => "your_other_database_prefix_", :suffix => "_is_legacy")
Even though it might not be the best place for it, I put this in my test_helper. You don't want it to execute for every test, so put something like this around it:
unless defined?(CLONED_OTHER_DB_FOR_TESTING) UseDbTestSetup.prepare_test_db(:prefix => "your_other_database_prefix_", :suffix => "_is_legacy") CLONED_OTHER_DB_FOR_TESTING = true end
Add this statement in your test_helper or whereever you like such things.
UseDb.debug_print = true
Nope. I don't use them and you probably shouldn't either, so this gem doesn't support them. See factory_girl.
Have a change or improvement? Fork it, fix it, then send a pull request.
David Stevenson (email@example.com) originally wrote the code for this as a plugin for Rails 2. I wanted it to be a gem for Rails 3, so that's what I did. I renamed a few things here and there, added some additional debugging statements, but it's largely what he wrote. Thanks David.