Maybe if this task is hard, you could do a simplier variant, "FROM Class1 a1 JOIN a1,a2 WITH a2 INSTANCE OF Class2"?
Doctrine 2.3 supports it, but in fact, it does not work. I can't use Class2 fields in query, and Doctrine ignores the INSTANCE OF operator when building a native queries.
I am working with system where I have many inherited classes with Class Table Inheritance. When I do a JOIN query, it generates native sql query more than 1KB(?!) length, and MySQL freezes for more than 7 minutes (?!) on it. It must join only tables for Class2, but it joins all my 20 tables inherited of my base class
I don't know where to send bugreport
It will be very good if I could manually select a joined class to make Doctrine do a better queries.
Sorry for my english, I am from Moscow.