Rails - Jan 2006 - If you want to disconnect a database properly, there is the code:)!!!

Hi, 

We have worked on a problem of connection: Connect to
two databases with a single ActiveRecord::Base model
class within the same action
The main difficulty is how to disconnect the actual
connection properly and then let the ActiveRecord
establishes a new one. 
The actual function "remove_connection" removes the
connection, but its doesn''t unbind the link between
rails and the database. 
So we decide to add some new methodes in order to
remove all link between rails and the database.

First, we added a new methode to the adapter, we are
using postgresql, the following code is written for
postgresql_adapter.rb
if you are using another database, you have to rewrite
it. In postgresql_adapter.rb, add the follong code

      def disconnect
	if (@connection != nil) then 
		# methode "close" is exported by the postgres.so for
disconnect the database
		@connection.close	
		@connection = nil	# clear the connection
	end
      end

In connection_specification.rb, add the following code
at the end (in the "ActiveRecord::Base" class section)

   def self.clear_connection(klass=self)
       @@defined_connections.delete(klass) 	# remove
the connection
       ac = active_connections 			# get the active
connection
       ac.delete(klass) if ac.kind_of?(Hash)    #
remove the connection	 
       self.connection.disconnect		# disconnect the
link with database, it call the newly added methode in
postgresql_adapter
       @connection = nil			# remove the connection
cached in the ActiveRecord::base class
   end

For the tests, we have used the following code:

	# first connection 
	GenTableAs.establish_connection(:adapter =>
"postgresql",
					:host => "1.2.3.4",
					:port => 5432,
					:database => "db1", 
					:username => "dbuser1", 
					:password => "dbuser1")
				
	GenTableAs.set_table_name ''table_no_1''
    	GenTableAs.reset_column_information()
    	obj1 = GenTableAs.new
    	@col1 = obj1.class.column_names()	

	obj1["colaa"] = 123
	obj1["colab"] = "123"
	obj1.save	
	obj1 = nil

	GenTableAs.clear_connection	# here we disconnect the
connection

	# connection to a new database
	GenTableAs.establish_connection(:adapter =>
"postgresql",
					:host => "9.8.7.5",
					:port => 5432, 												
					:database => "db2", 
					:username => "dbuser2", 
					:password => "dbuser2")

	GenTableAs.set_table_name "table_no_42"
    	GenTableAs.reset_column_information()
    	obj1 = GenTableAs.new
    	@col2 = obj1.class.column_names()

	obj1["col12"] = 456
	obj1["col34"] = "789"
	obj1.save
    	obj1 = nil
	GenTableAs.clear_connection	# here we disconnect
again the connection


It should give us the name of the columns of two
different tables of different database in @col1 and
@col2 and save the data to 
tables. 

So hope this will help who which to do the same thing,
(Actually, it takes us a few days to fully understand
the mecanism of the 
database connection:))

If anyone has any comments about this, please
communicate with us:)!!!! 

Thanks you very much

Saiho

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