There are distinctive reasons why you should think about having various databases in your Ruby on Rails application. In my situation, I expected to store large quantities of data.
Consider default database is MySQL. In our application database.yml file write connections for MySQL in normal way. After that, for connecting postgresql in the same application we need to create custom files.
Create the custom database files to connect postgresql
We’re going to set up a second database called “Stats”
First of all, create the file config/database_stats.yml and populate it as you do with the primary database’s config file.
Your file will look something like this:
development:
adapter: postgresql
encoding: utf8
reconnect: false
database: db_info_development
pool: 5
host: localhost
username: postgres
password:
We’re now going to create a directory that will hold the schema and all the migrations of the Stats database.
Create directory with name db_stats in the rails root and copy the structure as mentioned below
–db
–migrate
schema.rb
seeds.rb
–db_stats
–migrate
schema.rb
seeds.rb
The created files should be empty.
Add Rake Tasks
For handling stats database, we need to write custom tasks for creation, migrations and other functionalities.
Create a file lib/tasks/db_stats.rake with the below content
namespace :stats do
namespace :db do |ns|
task :drop do
Rake::Task[“db:drop”].invoke
end
task :create do
Rake::Task[“db:create”].invoke
end
task :setup do
Rake::Task[“db:setup”].invoke
end
task :migrate do
Rake::Task[“db:migrate”].invoke
end
task :rollback do
Rake::Task[“db:rollback”].invoke
end
task :seed do
Rake::Task[“db:seed”].invoke
end
task :version do
Rake::Task[“db:version”].invoke
end
namespace :schema do
task :load do
Rake::Task[“db:schema:load”].invoke
end
task :dump do
Rake::Task[“db:schema:dump”].invoke
end
end
namespace :test do
task :prepare do
Rake::Task[“db:test:prepare”].invoke
end
end
# append and prepend proper tasks to all the tasks defined here above
ns.tasks.each do |task|
task.enhance [“stats:set_custom_config”] do
Rake::Task[“stats:revert_to_original_config”].invoke
end
end
end
task :set_custom_config do
# save current vars
@original_config = {
env_schema: ENV[‘SCHEMA’],
config: Rails.application.config.dup
}
# set config variables for custom database
ENV[‘SCHEMA’] = “db_stats/schema.rb”
Rails.application.config.paths[‘db’] = [“db_stats”]
Rails.application.config.paths[‘db/migrate’] = [“db_stats/migrate”]
Rails.application.config.paths[‘db/seeds’] = [“db_stats/seeds.rb”]
Rails.application.config.paths[‘config/database’] = [“config/database_stats.yml”]
end
task :revert_to_original_config do
# reset config variables to original values
ENV[‘SCHEMA’] = @original_config[:env_schema]
Rails.application.config = @original_config[:config]
end
end
Once all of this setup is done, we can create the stats database and run its first migration:
$ rake stats:db:create
$ rake stats:db:migrate
This will generate the Stats database schema file in db_stats/schema.rb.
Add a custom migration generator
We cannot use rails generator because the path hardcodes the db/migrate. Therefore, we need to have custom generator to create all migrations for the stats database.
Create the generator in lib/generators/stats_migration_generator.rb and paste the following code:
require ‘rails/generators/active_record/migration/migration_generator’
class StatsMigrationGenerator < ActiveRecord::Generators::MigrationGenerator
source_root File.join(File.dirname(ActiveRecord::Generators::MigrationGenerator. instance_method(:create_migration_file) .source_location.first), “templates”)
def create_migration_file
set_local_assigns!
validate_file_name!
migration_template @migration_template, “db_stats/migrate/#{file_name}.rb”
end
end
With all of this in place, we can now generate migrations for the Stats database:
$ rails g stats_migration migration_name
This migration file gets created in the stats database migrate directory db_stats/migrate.
After that, run the following command to migrate.
$ rake stats:db:migrate
Finalize connection and models for PostgreSQL
We’re almost done. Add a new initializer file config/initializers/db_stats.rb and paste the following:
# save stats database settings in global var
DB_STATS = YAML::load(ERB.new(File.read(Rails.root.join(“config”,”database_stats.yml”))).result)[Rails.env]
Configuring mongodb:
Mongoid gem is an ODM (Object-Document-Mapper) framework for MongoDB in Ruby.
gem ‘mongoid’, ‘~> 5.1.0’
You can generate a config file by executing the generator. Mongoid will then handle everything else from there.
$ rails g mongoid:config
Then it creates mongoid.yml as below
development:
clients:
default:
database: mongoid
hosts:
-localhost:27017
Now in our application we have successfully integrated the MySQL, postgresql and mongodb
Consider three models – User, Product, Image. Using these three models will help us connect different databases in our application.
User model with MySQL connection
class User < ActiveRecord::Base
end
$ rails g migration create_users field_names
rake db:migrate
This migration file gets created under db/migrate and it will store under MySQL database.
class Product < ActiveRecord::Base
establish_connection DB_STATS
end
$ rails g stats_migration create_products
create db_stats/migrate/20151201191642_create_products.rb
This migration file gets created in the stats database migrate directory db_stats/migrate.
class Image
include Mongoid::Document
field :name, type: String
field :description, type: String
end
No need for running any migrations for mongodb since it is ODM. This data is created under MongoDB.
Feel free to contact us if you have any query.