zend framework using mysql_real_escape_string in 2 tier server

In one of my application I'm using zend framework. web/applicati开发者_Go百科on server, database server are physically different. now i'm using mysql_real_escape_string for security where i am giving first parameter. and it gives me an warning "link_identifier not found or no database connection identifier".

when i created a connection identifier for that instance and provided it stared working. my question is why it is not identifying it on its own.

By default, all methods in Zend_Db_Adapter will escape your input. So mysql_real_escape_string is superfluous