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Editorial Team
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Asked: 2026-05-13T10:03:54+00:00

There are four classes: StudentBase , CourseBase and StudentDataMapper , CourseDataMapper An Student object

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There are four classes:

StudentBase, CourseBase and
StudentDataMapper, CourseDataMapper

An Student object can have a relationship with an Course object. One Student can have many courses. One course can be visited by many students.

In the ER diagram, a Student entity has an attribute called “courses”, but a course does not know anything about his students. A course has no Attribute called “students” in return.

Which of these classes should perform the creation of the relationship?

EDIT: This is the System Layer! In the Business Logic Layer, the developer subclasses StudentBase and CourseBase to create a Student class and an Course class. The developer who creates these classes will not see any of that code, except for his own business logic code.

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  1. Editorial Team

    Neither.

    First, the ERD should change; what you’ve described is a many-to-many relationship (a course can have many students and a student many courses). So, the student shouldn’t have a courses attribute but, instead, there should be a student-course entity.

    Then there should be a StudentCourseDataMapper class that does what you’re asking (maintaining relationships) and both StudentDataMapper and CourseDataMapper should be aware of and use it.

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