Using Postgresql along with MySql

I came across a scenario where my existing application database which was residing in MySql wanted to create/communicate to tables present in PostgreSql. Though it is not advisable but i had no other option. so i googled a lot, went through n number of blogs and finally found a solution which suited my requirement this worked for me.

Install PostgreSql has explained in my previous post.

Configure your database.yml

development:
  adapter: mysql2
  encoding: utf8
  database: test_development
  username: root
  password: *******
  host: 127.0.0.1


development_postgres:
  adapter: postgresql
  database: test_dev
  username: pgs_root
  password: ********
  host: 127.0.0.1


Create the database

rake db:create RAILS_ENV=development_postgres

This will create a database named test_dev in PostgreSQL

Specify the connection in model so that the application understands where the table resides

establish_connection :development_postgres

if you wish to have it environment specific, write

establish_connection Rails.env+"_postgres"


In migration file, specify the connection

def self.connection
  modelname.connection
end
def self.up
      
end

   This self.connection allows the application to communicate with database specified in the model. This has to be written only if you want to run migration belonging to postgres, failing to specify migration will run in default database i.e mysql

Establishing relationship between the tables present in two databases

for ex. table named "foo" exists in postgres and it belongs to "boo" present in mysql.

In foo.rb

establish_connection Rails.env  (relationship  database connection)
belongs_to :boo
establish_connection Rails.env+"_postgres" (database connection)

In boo.rb

establish_connection Rails.env+"_postgres"
has_many  :foo
establish_connection Rails.env

This establishes HasManyBelongsTo relationship between boo & foo.
Note:Always Specify the relationship database connection first & table connection at the end. All the migration no. will be stored in schema_migration table present in mysql.


This is the only approach which worked for me, if there is a better solution other than the above please let me know.