Being a tagging freak, I wanted to coalesce my database of tagged tables with typo’s nascent support of tags. Only problem: both use ‘tags’ as the tag table name.

My choices were to either:

• change the name of my tags table and all its joining tables as well as a hefty amount of code I’ve written for those tables
• simply extend typo to connect to two databases.

I chose the latter.

Since I was defining more table classes, I made another model file under app/models/ ( called url.rb for me). I then made sure the controller I was using aware of my model file by giving it a model declaration:

class ArticlesController < ApplicationController
  model :article,:url
  #all other code
  # ...
end

Note that I have to explicitly define the article model which was implicit until I used :model.

So what did I put in my model class?

From reading the rails wiki and the ActiveRecord API I found out that any table class can establish its own database connection via :establish_connection. So I wrote the following

class MyTags < ActiveRecord::Base
  establish_connection({
   :adapter  => "mysql",
   :username => "bozo",
   :password => "bogus",
   :database => "tags"
   })
   set_table_name "tags"
end

Soon enough I wanted to have a couple of tables that used my second database. From the ActiveRecord API, I read that subclasses of a table class share the same connection so I figured I’d make an abstract connection class for all the tag tables. So I tried the following

class TagsDB < ActiveRecord::Base
  establish_connection({
   :adapter  => "mysql",
   :username => "bozo",
   :password => "bogus",
   :database => "tags"
   })
end

class MyTags < TagsDB
   set_table_name "tags"
end

class Url < TagsDB
end

Wrong, instead I got this error:

ActiveRecord::StatementInvalid (Table ‘tags.tags_a_rs’ doesn’t exist: SHOW FIELDS FROM tags_a_rs)

I was able to get the above code to work only by making the parent class a valid table and redefining the subclasses’ table names. Since it seemed poor design to have tables inherit more than they should (table name, relationships and who knows what else) for a database connection, I reverted to defining the connection for every class:

$tags_connection = {
   :adapter  => "mysql",
   :username => "bozo",
   :password => "bogus",
   :database => "tags"
}

class MyTags < ActiveRecord::Base
  establish_connection $tags_connection
  set_table_name "tags"
end

class Url
  establish_connection $tags_connection
end

This is the cleanest solution I found from what I understand of subclassing table classes.