Rails Engines with multiple databases - mysql

Question

I am creating application in Ruby on Rails which is having many engines(for modularity).
I want different databases for each engine. How to configure this?
Database - MYSQL

Answer 1

There is a good explanation by the link http://www.blrice.net/blog/2016/04/09/one-rails-app-with-many-databases/

Answer 2

General approach is to take a look at the framework sources and decide can it be reused.
Let's take a look at activerecord/lib/active_record/railties/databases.rake (v5.0.7) first. For example on how db:create implemented.
We will see ActiveRecord::Tasks::DatabaseTasks.create_current.
Let's open ActiveRecord::Tasks::DatabaseTasks and take a look at
# The possible config values are:
#
# * +env+: current environment (like Rails.env).
# * +database_configuration+: configuration of your databases (as in +config/database.yml+).
# * +db_dir+: your +db+ directory.
# * +fixtures_path+: a path to fixtures directory.
# * +migrations_paths+: a list of paths to directories with migrations.
# * +seed_loader+: an object which will load seeds, it needs to respond to the +load_seed+ method.
# * +root+: a path to the root of the application.
#
# Example usage of DatabaseTasks outside Rails could look as such:
#
# include ActiveRecord::Tasks
# DatabaseTasks.database_configuration = YAML.load_file('my_database_config.yml')
# DatabaseTasks.db_dir = 'db'
# # other settings...
This way we are getting to following solution:
namespace :your_engine do
namespace :db do
task :load_config do
ActiveRecord::Tasks::DatabaseTasks.database_configuration = YAML.load_file("config/database_your_engine.yml")
ActiveRecord::Tasks::DatabaseTasks.db_dir = "db_your_engine"
ActiveRecord::Tasks::DatabaseTasks.migrations_paths = [ "components/your_engine/db/migrate" ]
ActiveRecord::Base.configurations = ActiveRecord::Tasks::DatabaseTasks.database_configuration
ActiveRecord::Migrator.migrations_paths = ActiveRecord::Tasks::DatabaseTasks.migrations_paths
# You can observe following values to see how settings applied.
# puts ActiveRecord::Base.configurations
# puts ActiveRecord::Migrator.migrations_paths
# puts ActiveRecord::Tasks::DatabaseTasks.database_configuration
# puts ActiveRecord::Tasks::DatabaseTasks.migrations_paths
end
desc "Create Your DB"
task create: :load_config do
ActiveRecord::Tasks::DatabaseTasks.create_current
end
end
end
The same approach for drop/migrate and other needed tasks.
It is good general rule - know you stack at least one level lower than your work with. Sometimes reading underlying sources much more helpful than direct answer.
I will update this answer while going forward with my solution...