gistfile1.rb

# This is a blog post I wrote almost two years ago. It was some of the first Ruby I ever uttered, and not
# entirely useful or elegant, but I'm reposting it now because I recently received a requst for it.



# Ruby on Rails: Working With a Legacy Database With a Non-Integer Primary Key

# For a project I'm currently working on, I needed to get my Rails application to work with a legacy 
# database that used a non-integer primary key (in this case, a field called "loginID", which is basically
# a username). First, I tried to use "set_primary_key" to define my PK, but Rails was having none of that.
# Instead, I decided to write a couple of custom methods for my legacy class.

# To connect to the legacy database, I first added the following configuration to the end of my
# config/database.yml file:

# legacy database info
legacy_db:
  adapter: mysql
  database: legacy_database_name
  username: user
  password: pass
  host: localhost

# Once my database credentials were defined, I set up my LegacyUser class to use the legacy_db
# connection, and wrote custom update and delete methods. The update method takes a hash, just
# like the <a href="http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M001044">ActiveRecord method
# update_attributes</a>. It goes through this hash and updates each attribute in the legacy database as
# appropriate.

class LegacyUser < ActiveRecord::Base
  
  set_table_name "legacy_user_table"
  establish_connection :legacy_db
  
  validates_uniqueness_of :loginID
  
  def update(var)
  	query = "UPDATE legacy_user_table SET "
  	query += var.keys.map{ |k| %%#{k.to_s} = "#{var[k]}"% }.join(", ")
  	query += %% WHERE loginID = "#{self.loginID}"%
  	
  	LegacyUser.connection.execute query
  end
  
  def delete
  	LegacyUser.connection.execute %%DELETE FROM legacy_user_table WHERE loginID = "#{self.loginID}"%
  end
  
end

# There may be a cleaner way to do this, but nothing I tried worked with this particular database.
# If you find yourself having to write some custom SQL functions as a last resort, hopefully this
# example will have given you a good place from which to start.

# As with most of the Rails things I do, thanks to <a href="http://www.napcsweb.com/">Brian Hogan</a>
# for helping me out with this.