Android : How to use whereMatchesKeyInQuery with pointer to class

I call them tables but in the code they are actually just classes. I got table of users (class that extends ParseUser) I got table TableAClass (class that extends ParseObject), and I got table TableBClass (class that extends ParseObject) B contains pointers to MyUserClass and to TableAClass

ParseQuery<MyUserClass> query = ParseQuery.getQuery(MyUserClass.class);


ParseQuery<TableBClass> secondQuery = new ParseQuery<TableBClass>(
                    MyInstallsClass.class);

now the key part, I can't query like this

query.whereMatchesKeyInQuery( "objectId", "myuser_id",secondQuery);

because 'myuser_id' is not an String it is a Pointer to MyUserClass How should I make this query work without adding additional String columns with of String type that will contain the objectId