correct management of repository in clean architecture - clean-architecture

Question

I´m new to implementing clean architecture although I really like the concept, however, when I think of repository implementation I'm always unsure.
For example: I always find diagrams like this
In these diagrams, the repository interfaces use the entities and the entities know nothing about anything. The thing is I think it may be more useful for entities to be conscious of repository interfaces instead. I think it wouldn't violate the inversion of control principle since they are just interfaces and not implementations.
an example (not real code or language because language is not important in this case):
Class StudentEntity:
important method: getMathGrade
Class MathClassroomEntity:
constructor(repository){
this.repo = repository
}
important method: getStudents(){
this.repo.getStudents()
}
important method: getAverageGrade(){
students = this.getStudents()
sum = 0
foreach student in students:
sum = student.getMathGrade()
return sum/students.length
}
As you can see, many important business logic in one entity is related to other entities.
if the entities don't know anything about repos (interfaces at least).
how can I put these methods in my entities?
should I make my entities abstract? which I think is not so pretty
should I put this business logic in my use cases? which sounds even worse
why do they make repo interfaces use entities and not the other way? what are the advantages?
I know this is a lot, so thanks a lot in advance

Answer 1

how can I put these methods in my entities?
You don't need to put these methods in your entities.
The use case queries the repository and the repository should return the MathClassroomEntity which should just contain the students.
class RepositoryImpl implements Repository {
public MathClassroom getMathClassroom(){
return new MathClassroom(getStudents);
}
private List<Student> getStudents(){
return .....;
}
}
Thus the MathClassroom will only know about students
public class MathClassroom {
private List<Student> students;
public MathClassroom(List<Student> students){
this.students = students;
}
public double getAverageGrade(){
double sum = 0;
for(Student student : students){
sum += student.getMathGrade()
}
return sum / students.size();
}
}
Easy to test and decoupled from the repository.