Question

My Rails 3.2 app use two different databases. The main os is a MySQL while the oher is a sqlserver DB :

development:
    adapter: mysql2
    encoding: utf8
    database: mydb
    username: myuser
    password: ***
secondbase:
    adapter: sqlserver
    database: anotherbase
    username: anotheruser
    password: ***

I have two associated models :

class Account < ActiveRecord::Base
    establish_connection :secondbase
    has_many :docs
end

class Docs < ActiveRecord::Base
    belongs_to :account
end

Since the two model use table on two differents database, I suppose I can’t use eager_loading and load associated data with join or includes

But I think preload should still allow me to load the data using two queries (instead of N + 1)

However, when trying to use preloadin my controller, it raises an error :

Docs.where(someconditions).preload(:account)

returns

Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'USE [anotherbase]

What could I do to preload the Account data and avoid N + 1 queries when dusplaying the Docs with some Account details in my views ?

Answer 1

Have you looked at Apartment gem: https://github.com/bradrobertson/apartment ?

It provides you the means to deal with multiple databases.