Rails 3 - Multiple database with joins condition

Question

My environment: Ruby 1.9.2p290, Rails 3.0.9 and RubyGem 1.8.8

unfortunately I have an issue when come across multiple database.

The situation is this: I have two model connect with two different database and also establishing association between each other. database connection specifying in each model, look likes

class Visit < ActiveRecord::Base
  self.establish_connection "lab"
  belongs_to :patient
end

class Patient < ActiveRecord::Base
  self.establish_connection "main"
  has_many :visits
end

I got an error when meet following scenario

@visits = Visit.joins(:patient)

Errors: Mysql2::Error: Table 'lab.patients' doesn't exist: SELECT visits.* FROM visits INNER JOIN patients ON patients.id IS NULL

Here 'patients' table is in 'main' database and 'visits' table in 'lab' database I doubt when executing the code, that Rails is considering 'patients' table is part of 'lab' database [which holds 'visits' table].

Answer 1

Well, I don't know if this is the most elegant solution, but I did get this to work by defining self.table_name_prefix to explicitly return the database name.

class Visit < ActiveRecord::Base
  def self.table_name_prefix
    renv = ENV['RAILS_ENV'] || ENV['RACK_ENV']
    (renv.empty? ? "lab." : "lab_#{renv}.")
  end

  self.establish_connection "lab"
  belongs_to :patient
end

class Patient < ActiveRecord::Base
  def self.table_name_prefix
    renv = ENV['RAILS_ENV'] || ENV['RACK_ENV']
    (renv.empty? ? "main." : "main_#{renv}.")
  end

  self.establish_connection "main"
  has_many :visits
end

I'm still working through all the details when it comes to specifying the join conditions, but I hope this helps.

Answer 2

Might be cleaner to do something like this:

  def self.table_name_prefix
    "#{Rails.configuration.database_configuration["#{Rails.env}"]['database']}."
  end

That will pull the appropriate database name from your database.yml file