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Lets say I have a User with 2 derived entities Student , Teacher . I used the TPH method, so I actually have no property at all in my classes to tell me who is a teacher or not. I have 2 booleans that should allow me to load either student or teacher such as this: //IQueryable<User> var query = userRepository.GetUsers(); //Type filtering if (searchModel.IsStudent) { query = query.OfType<Student>(); } if (searchModel.IsTeacher) { query = query.OfType<Teacher>(); } When this tries to evaluate, I get this error when both are true: DbIsOfExpression requires an expression argument with a polymorphic result type that is compatible with the type argument. I already looked at some answers here on SO but they are geared towards 1 type of filtering. I would then like to do something like this (rough coding): if(query.ToList().FirstOrDefault() is Student) { print "student"; } The mapping: protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<User>() .Map<Teacher>(m => m.Requires("UserType").HasValue("Teach")) .Map<Student>(m => m.Requires("UserType").HasValue("Stu")) .Map<Staff>(m => m.Requires("UserType").HasValue("Staff")); }

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