Fix ManyToMany Realation Courses-Students and OneToMany Teacher-Courses

Add Annotations in Course, Student and Teacher for the Relations
Add Methods in CourseRepository that find a Course and fill the Students and Teacher from Foreign Keys
Add Fix findById and findAll in CourseService accordingly to the new Methods in CourseRepository

core/src/main/java/studentmanagement/service/administrator/DefaultAdministratorService.java

@@ -31,12 +31,12 @@ public class DefaultAdministratorService implements AdministratorService {
     }
 
     @Override
-    public StudentCourseResponse enroll(StudentCourseIdRequest dto) { //TODO: Fix Many to Many
+    public StudentCourseResponse enroll(StudentCourseIdRequest dto) {
         return findByIdExecuteAndSave(dto, (s, c) -> c.enroll(s));
     }
 
     @Override
-    public StudentCourseResponse dismiss(StudentCourseIdRequest dto) {//TODO: Fix Many to Many
+    public StudentCourseResponse dismiss(StudentCourseIdRequest dto) {
         return findByIdExecuteAndSave(dto, (s, c) -> c.dismiss(s));
     }
 
@@ -58,8 +58,8 @@ public class DefaultAdministratorService implements AdministratorService {
 
         executor.accept(student, course);
 
-        courseService.save(course); //TODO: Fix Many to Many
-        studentService.save(student); //TODO: Fix Many to Many
+        courseService.save(course);
+        studentService.save(student);
 
         return new StudentCourseResponse(student, course);
     }
@@ -72,7 +72,7 @@ public class DefaultAdministratorService implements AdministratorService {
         executor.accept(teacher, course);
 
         courseService.save(course);
-        //        teacherService.save(teacher);
+        teacherService.save(teacher);
 
         return new TeacherCourseResponse(teacher, course);
     }

core/src/main/java/studentmanagement/service/course/DefaultCourseService.java

@@ -5,10 +5,14 @@ import org.springframework.stereotype.Service;
 import studentmanagement.data.course.CourseRepository;
 import studentmanagement.model.course.Course;
 import studentmanagement.model.dto.create.CourseCreateRequest;
+import studentmanagement.model.key.IDableKey;
 import studentmanagement.model.person.teacher.Teacher;
+import studentmanagement.service.course.exception.CourseDoesNotExistException;
 import studentmanagement.service.generic.DefaultService;
 import studentmanagement.service.teacher.TeacherService;
 
+import java.util.Collection;
+
 @Service
 public class DefaultCourseService extends DefaultService<Course> implements CourseService {
     private final TeacherService teacherService;
@@ -30,4 +34,15 @@ public class DefaultCourseService extends DefaultService<Course> implements Cour
         teacherService.save(teacher);
         return save(course);
     }
+
+    @Override
+    public Course findById(IDableKey key) {
+        return ((CourseRepository) repository).findCourseWithStudentsAndTeacherById(key.id())
+            .orElseThrow(() -> new CourseDoesNotExistException("Course with " + key + " does not exist"));
+    }
+
+    @Override
+    public Collection<Course> findAll() {
+        return ((CourseRepository) repository).findAll();
+    }
 }
\ No newline at end of file

core/src/main/java/studentmanagement/service/course/exception/CourseDoesNotExistException.java

 package studentmanagement.service.course.exception;
 
-public class CourseDoesNotExistException extends Exception {
+public class CourseDoesNotExistException extends RuntimeException {
     public CourseDoesNotExistException(String message) {
         super(message);
     }

core/src/main/java/studentmanagement/service/grade/DefaultGradeService.java

@@ -5,6 +5,7 @@ import org.springframework.stereotype.Service;
 import studentmanagement.data.grade.GradeRepository;
 import studentmanagement.model.course.Course;
 import studentmanagement.model.course.dto.CourseStudentListResponse;
+import studentmanagement.model.course.exception.StudentNotInCourseException;
 import studentmanagement.model.dto.create.AddGradeRequest;
 import studentmanagement.model.dto.create.StudentCourseIdRequest;
 import studentmanagement.model.grade.Grade;
@@ -107,6 +108,11 @@ public class DefaultGradeService implements GradeService {
         Student student = studentService.findById(dto.studentKey());
         Course course = courseService.findById(dto.courseKey());
 
+        if (!course.isEnrolled(student)) {
+            throw new StudentNotInCourseException(
+                "Student with ID:" + student.getId() + " is not enrolled in this Course");
+        }
+
         Grade toAdd = new Grade(student, course, grade);
 
         save(toAdd);
@@ -144,7 +150,10 @@ public class DefaultGradeService implements GradeService {
 
     @Override
     public Double findAverageForStudentInCourse(StudentCourseIdRequest dto) {
-        return null;
+        Collection<Grade> grades =
+            gradeRepository.findAllByStudentIdAndCourseId(dto.studentKey().id(), dto.courseKey().id());
+
+        return average(grades);
     }
 
     @Override

core/src/main/java/studentmanagement/service/grade/GradeService.java

@@ -10,8 +10,6 @@ import studentmanagement.model.key.IDableKey;
 import java.util.Collection;
 
 public interface GradeService {
-    //    StudentCourseResponse add(StudentCourseIdRequest dto);
-
     Grade save(Grade grade);
 
     Collection<Grade> saveAll(Collection<Grade> grades);

data/src/main/java/studentmanagement/data/course/CourseRepository.java

 package studentmanagement.data.course;
 
+import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.stereotype.Repository;
 import studentmanagement.model.course.Course;
 
+import java.util.List;
+import java.util.Optional;
+
 @Repository
 public interface CourseRepository extends JpaRepository<Course, Long> {
+    @EntityGraph(attributePaths = {"students", "teacher"})
+    Optional<Course> findCourseWithStudentsAndTeacherById(Long id);
 
+    @EntityGraph(attributePaths = {"students", "teacher"})
+    List<Course> findAll();
 }

data/src/main/java/studentmanagement/data/student/StudentRepository.java

@@ -6,5 +6,4 @@ import studentmanagement.model.person.student.Student;
 
 @Repository
 public interface StudentRepository extends JpaRepository<Student, Long> {
-
 }
\ No newline at end of file

model/src/main/java/studentmanagement/model/DefaultIDable.java

@@ -10,6 +10,7 @@ import jakarta.persistence.MappedSuperclass;
 public class DefaultIDable implements IDable {
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
+    @Column(nullable = false)
     private Long id;
 
     @Column
@@ -23,15 +24,15 @@ public class DefaultIDable implements IDable {
         this.name = name;
     }
 
-    public void setId(Long id) {
-        this.id = id;
-    }
-
     @Override
     public Long getId() {
         return id;
     }
 
+    public void setId(Long id) {
+        this.id = id;
+    }
+
     @Override
     public String getName() {
         return name;

model/src/main/java/studentmanagement/model/course/Course.java

 package studentmanagement.model.course;
 
+import jakarta.persistence.CascadeType;
 import jakarta.persistence.Column;
 import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.JoinTable;
 import jakarta.persistence.ManyToMany;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.Table;
+import org.hibernate.Hibernate;
 import studentmanagement.model.DefaultIDable;
 import studentmanagement.model.course.exception.StudentAlreadyInCourseException;
 import studentmanagement.model.course.exception.StudentNotInCourseException;
@@ -24,23 +29,20 @@ public class Course extends DefaultIDable implements Comparable<Course> {
     @Column
     private long totalHours;
 
-    //TODO Fix Many to Many
-    //    @ManyToMany(fetch = FetchType.LAZY,
-    //        cascade = {
-    //            CascadeType.PERSIST,
-    //            CascadeType.MERGE
-    //        })
-    //    @JoinTable(name = "course_students",
-    //        joinColumns = {@JoinColumn(name = "course_id")},
-    //        inverseJoinColumns = {@JoinColumn(name = "student_id")})
-    @ManyToMany
-    private Set<Student> students;
-
-    @ManyToOne
+    @ManyToMany(fetch = FetchType.LAZY,
+        cascade = {
+            CascadeType.PERSIST,
+            CascadeType.MERGE
+        })
+    @JoinTable(name = "course_students",
+        joinColumns = {@JoinColumn(name = "course_id", referencedColumnName = "id")},
+        inverseJoinColumns = {@JoinColumn(name = "student_id", referencedColumnName = "id")})
+    private Set<Student> students = new HashSet<>();
+
+    @ManyToOne(fetch = FetchType.LAZY)
     private Teacher teacher;
 
     public Course() {
-        students = new HashSet<>();
     }
 
     public Course(String name, long totalHours, Teacher teacher) {
@@ -68,6 +70,10 @@ public class Course extends DefaultIDable implements Comparable<Course> {
 
     public void employ(Teacher teacher) {
         this.teacher = teacher;
+
+        if (Hibernate.isInitialized(teacher.getCourses())) {
+            teacher.getCourses().add(this);
+        }
     }
 
     public void fire(Teacher teacher) throws TeacherNotInCourseException {
@@ -75,6 +81,10 @@ public class Course extends DefaultIDable implements Comparable<Course> {
             throw new TeacherNotInCourseException("Teacher: " + teacher + " is no employed in this Course");
         }
         this.teacher = null;
+
+        if (Hibernate.isInitialized(teacher.getCourses())) {
+            teacher.getCourses().remove(this);
+        }
     }
 
     /**
@@ -84,12 +94,12 @@ public class Course extends DefaultIDable implements Comparable<Course> {
      * @throws StudentAlreadyInCourseException - if the Student is already in the Course
      */
     public Student enroll(Student student) {
-        if (students.isEmpty()) {
-            students = new HashSet<>();
-        }
-
         students.add(student);
 
+        if (Hibernate.isInitialized(student.getCourses())) {
+            student.getCourses().add(this);
+        }
+
         return student;
     }
 
@@ -98,6 +108,10 @@ public class Course extends DefaultIDable implements Comparable<Course> {
 
         students.remove(student);
 
+        if (Hibernate.isInitialized(student.getCourses())) {
+            student.getCourses().add(this);
+        }
+
         return student;
     }
 

model/src/main/java/studentmanagement/model/person/student/Student.java

@@ -2,21 +2,20 @@ package studentmanagement.model.person.student;
 
 import jakarta.persistence.Column;
 import jakarta.persistence.Entity;
+import jakarta.persistence.ManyToMany;
 import jakarta.persistence.Table;
+import studentmanagement.model.course.Course;
 import studentmanagement.model.person.Person;
 
+import java.util.HashSet;
+import java.util.Set;
+
 @Entity
 @Table(name = "Students")
 public class Student extends Person {
 
-    //TODO Fix Many to Many
-    //    @ManyToMany(fetch = FetchType.LAZY,
-    //        cascade = {
-    //            CascadeType.PERSIST,
-    //            CascadeType.MERGE
-    //        },
-    //        mappedBy = "students")
-    //    private Set<Course> courses;
+    @ManyToMany(mappedBy = "students")
+    private transient Set<Course> courses = new HashSet<>();
 
     @Column
     private long age;
@@ -29,6 +28,10 @@ public class Student extends Person {
         this.age = age;
     }
 
+    public Set<Course> getCourses() {
+        return courses;
+    }
+
     public long getAge() {
         return age;
     }

model/src/main/java/studentmanagement/model/person/teacher/Teacher.java

@@ -2,15 +2,23 @@ package studentmanagement.model.person.teacher;
 
 import jakarta.persistence.Column;
 import jakarta.persistence.Entity;
+import jakarta.persistence.OneToMany;
 import jakarta.persistence.Table;
+import studentmanagement.model.course.Course;
 import studentmanagement.model.person.Person;
 
+import java.util.HashSet;
+import java.util.Set;
+
 @Entity
 @Table(name = "Teachers")
 public class Teacher extends Person {
     @Column
     private Degree degree;
 
+    @OneToMany(mappedBy = "teacher")
+    private transient Set<Course> courses = new HashSet<>();
+
     public Teacher() {
 
     }
@@ -20,6 +28,10 @@ public class Teacher extends Person {
         this.degree = degree;
     }
 
+    public Set<Course> getCourses() {
+        return courses;
+    }
+
     public Degree getDegree() {
         return degree;
     }