I have a polymorphic association (Class Table Inheritance) and I need use DQL to query entities of a specific child class wich can be done using "x INSTANCE OF Entity" in WHERE clause. Now I need to put conditions specific for that child class but I get this error: "Class Person has no association named student_field_1" Person = Parent Class Employee = Child class Student = Child class is there any way yo cast of somehow tell Doctrine that the Person is actually a Student and to allow me to put Student fields in the WHERE?