Rails: using set_table_name to join across different databases on the same mysql server

Question

For legacy reasons, my model's tables are stored in two different databases on the same MySQL server. At first I just used establish_connection to specify the second database on the models that used it. However, when I established a has_many :through connection between two models in different databases, it blew up because MySQL cannot JOIN across two different servers. Then I noticed on the interwebs that I could use set_table_name 'other_database.foos' instead of using establish_connection.

This mostly works, but table_exists? always returns false even when the table does exist, and a couple of the plugins I'm using use that function extensively.

Is this a bug in table_exists?, or am I misusing set_table_name? Is there another way of doing what I'm trying to do?

Answer 1

table_exists? does the following:

def table_exists?(table_name)
  tables.include?(table_name.to_s)
end

Where tables is an array of the table names for the established connection (defined in databases.yml). So if you call table_exists?('database.table_name') or table_exists?('table_name_from_second_database') then it will always return false.

The only way around this would be to monkey patch table_exists? or the function that loads the tables array. See the api docs to see where to start with the patching.

Good Luck!