Merging Rails databases

Question

I have two databases with the same structure. The tables have an integer as a primary key as used in Rails.

If I have a patients table, I will have one patient using primary key 123 in one database and another patient using the same primary key in the other database.

What would you suggest for merging the data from both databases?

Answer 1

Set both your databases up with entries in config/database.yml, then generate a new migration.

Use ActiveRecord::Base.establish_connection to switch between the two databases in the migration like this:

def self.up
  ActiveRecord::Base.establish_connection :development
  patients = Patient.find(:all)
  ActiveRecord::Base.establish_connection :production
  patients.each { |patient| Patient.create patient.attributes.except("id") }
end

YMMV depending on the number of records and the associations between models.