Question

I have three entities as shown below.

Student { StudentID, Name, Age } 

Parent { ParentID, Name, Age } 

StudentParent { StudentParentID, StudentID, ParentID }

I need to get an IQueryable list of students that are a certain age and have no parents. I am currently using the following code which does work.

IQueryable<Student> Student s = from s in db.Students
                                 where s.Age == 18
                                 where !(from sp in db.StudentParent where sp.StudentID == s.StudentID select sp.StudentID).Contains(s.StudentID)
                                 select s;

I would just like help converting this to a Lambda expression.

Answer 1

This should work:

db.Students.Where( s =>
    s.Age == 18 &&  db.StudentParent.All(sp => sp.StudentID != s.StudentID)
);

Edit: This assumes that you do not have a link from students to parents; if you do, use it instead of a join for better readability.