title: Creating Relationships between collections in MongoDB
body: <p>I am new to MongoDB and I am creating a database to keep records of students and the courses that the students are doing at a university.
  There are three collections called Student, Subject and Lecturer.
  The Student collection contains studentId, name,dob,email,year.
  The  Subject collection contains the subjectId, subjectName,credits
  The Lecturer collection contains the lecturerId, lectureName, speciliazation, contactNo, email.
  The relationship between Student and Student collection is many to many.
  Between Subject and the Lecturer collection there is a one to one relationship.
  I need to add the subjectId to the student collection and lecturerId to the subject collection..
  Can anyone please tell me how can I create foreign key relationships between collections?</p>