development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: main_development
  pool: 5
  username: root
  password:
  socket: /var/run/mysqld/mysqld.sock

test:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: main_test
  pool: 5
  username: root
  password:
  socket: /var/run/mysqld/mysqld.sock

production:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: main_prod
  pool: 5
  username: root
  password:
  socket: /var/run/mysqld/mysqld.sock

class CreateRetailerToDomains < ActiveRecord::Migration

      def connection
        ActiveRecord::Base.establish_connection(
        :adapter => "mysql2",
        :encoding => "utf8",
        :reconnect => false,
        :database => "peripheral",
        :pool => 5,
        :username => "root",
        :password => "",
        :socket => "/var/run/mysqld/mysqld.sock").connection
      end

      def change
        ActiveRecord::Base.connection.create_table :retailer_to_domains do |t|
          t.string :name
          t.string :domain

          t.timestamps
        end
      end
    end

class RetailerToDomain < ActiveRecord::Base

 establish_connection(
            :adapter => "mysql2",
            :encoding => "utf8",
            :reconnect => false,
            :database => "peripheral",
            :pool => 5,
            :username => "root",
            :password => "",
            :socket => "/var/run/mysqld/mysqld.sock")

self.table=retailer_to_domain

validates_presence_of :name, :domain

end

Add another database connection seeting to database.yml file.

        database.yml file

            development:
              adapter: mysql2
              encoding: utf8
              reconnect: false
              database: main_development
              pool: 5
              username: root
              password:
              socket: /var/run/mysqld/mysqld.sock

            test:
              adapter: mysql2
              encoding: utf8
              reconnect: false
              database: main_test
              pool: 5
              username: root
              password:
              socket: /var/run/mysqld/mysqld.sock

            production:
              adapter: mysql2
              encoding: utf8
              reconnect: false
              database: main_prod
              pool: 5
              username: root
              password:
              socket: /var/run/mysqld/mysqld.sock

    another_database:
                adapter: "mysql2",
                encoding: "utf8",
                reconnect: false,
                database: "peripheral",
                pool: 5,
                username: "root",
                password: "",
                socket: "/var/run/mysqld/mysqld.sock"



Now In Migration file specify:
ActiveRecord::Base.establish_connection(:another_database)


class CreateRetailerToDomains < ActiveRecord::Migration
ActiveRecord::Base.establish_connection(:another_database)
 def change
     create_table :retailer_to_domains do |t|
          t.string :name
          t.string :domain

          t.timestamps
        end
      end
    end



 It will get create table inside that database only.


Model

class RetailerToDomain < ActiveRecord::Base
  ActiveRecord::Base.establish_connection(:another_database)
end


**To check the active database connection**
ActiveRecord::Base.connection.current_database