Все дописано, осталось наладить связи

src/main/java/ru/IP_LabWorks/IP/University/Model/Group.java

@@ -55,17 +55,15 @@ public class Group {
         return students;
     }
 
-    public void addStudent(Student student){
+    public void setStudents(List<Student> students) {
-        if (students == null)
+        this.students = students;
-            students = new ArrayList<>();
-        students.add(student);
     }
 
-    public List<Subject> getSubjects() { return subjects; }
+    public List<Subject> getSubjects(){
+        return subjects;
+    }
 
-    public void addSubject(Subject subject){
+    public void setSubjects(List<Subject> subjects) {
-        if (subjects == null)
+        this.subjects = subjects;
-            subjects = new ArrayList<>();
-        subjects.add(subject);
     }
 }

src/main/java/ru/IP_LabWorks/IP/University/Model/Subject.java

@@ -12,7 +12,7 @@ public class Subject {
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
     private String name;
-    @ManyToMany
+    @ManyToMany(fetch = FetchType.EAGER)
     private List<Group> groups;
 
     public Subject() {
@@ -47,8 +47,11 @@ public class Subject {
                 '}';
     }
 
-    public List<Group> getGroups() {
+    public List<Group> getGroups(){
         return groups;
     }
 
+    public void setGroups(List<Group> groups) {
+        this.groups = groups;
+    }
 }

src/main/java/ru/IP_LabWorks/IP/University/Service/GroupService.java

@@ -64,21 +64,33 @@ public class GroupService {
     }
 
     @Transactional
-    public Group deleteStudentInGroup(Long id, Student student) {
+    public void addStudentToGroup(Long groupId, Long studentId) {
-        final Group currentGroup = findGroup(id);
+        Group group = findGroup(groupId);
-        final Student currentStudent = em.find(Student.class, student.getId());
+        Student student = em.find(Student.class, studentId);
-        currentGroup.getStudents().remove(currentStudent);
+        if (group == null || student == null) {
-        em.merge(currentStudent);
+            throw new EntityNotFoundException("Group or Student not found");
-        return em.merge(currentGroup);
+        }
+        List<Student> students = group.getStudents();
+        if (!students.contains(student)) {
+            students.add(student);
+        }
+        group.setStudents(students);
+        em.merge(group);
     }
 
-    public List<Student> findStudentsInGroup(Long id){
+    @Transactional
-        final Group findGroup = findGroup(id);
+    public void removeStudentFromGroup(Long groupId, Long studentId) {
-        return findGroup.getStudents();
+        Group group = findGroup(groupId);
+        Student student = em.find(Student.class, studentId);
+        group.getStudents().remove(student);
     }
 
-    public List<Subject> findSubjectsInGroup(Long id){
+    @Transactional(readOnly = true)
-        final Group findGroup = findGroup(id);
+    public List<Student> findStudentsInGroup(Long groupId) {
-        return findGroup.getSubjects();
+        Group group = findGroup(groupId);
+        if (group == null) {
+            throw new EntityNotFoundException("Group not found");
+        }
+        return group.getStudents();
     }
 }

src/main/java/ru/IP_LabWorks/IP/University/Service/SubjectService.java

@@ -3,6 +3,7 @@ package ru.IP_LabWorks.IP.University.Service;
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.EntityNotFoundException;
 import jakarta.persistence.PersistenceContext;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.util.StringUtils;
@@ -16,6 +17,9 @@ public class SubjectService {
     @PersistenceContext
     private EntityManager em;
 
+    @Autowired
+    private GroupService groupService;
+
     @Transactional
     public Subject addSubject(String name){
         if (!StringUtils.hasText(name)) {
@@ -61,4 +65,30 @@ public class SubjectService {
     public void deleteAllSubjects() {
         em.createQuery("delete from Subject").executeUpdate();
     }
+
+    @Transactional
+    public void addGroupToSubject(Long subjectId, Long groupId) {
+        Subject subject = findSubject(subjectId);
+        Group group = groupService.findGroup(groupId);
+        subject.getGroups().add(group);
+        group.getSubjects().add(subject);
+        em.merge(subject);
+        em.merge(group);
+    }
+
+    @Transactional
+    public void removeGroupFromSubject(Long subjectId, Long groupId) {
+        Subject subject = findSubject(subjectId);
+        Group group = groupService.findGroup(groupId);
+        subject.getGroups().remove(group);
+        group.getSubjects().remove(subject);
+        em.merge(subject);
+        em.merge(group);
+    }
+
+    @Transactional(readOnly = true)
+    public List<Group> findGroupsBySubject(Long subjectId) {
+        Subject subject = findSubject(subjectId);
+        return subject.getGroups();
+    }
 }

src/test/java/ru/IP_LabWorks/IP/GroupServiceTests.java

@@ -71,10 +71,9 @@ public class GroupServiceTests {
         Student student1 = studentService.addStudent("Марков Данил Павлович", 19);
         Student student2 = studentService.addStudent("Емельянов Артём Сергеевич", 19);
         Group group = groupService.addGroup("ПИбд-21");
-        group.addStudent(student1);
+        groupService.addStudentToGroup(group.getId(), student1.getId());
-        group.addStudent(student2);
+        groupService.addStudentToGroup(group.getId(), student2.getId());
         final List<Student> students = groupService.findStudentsInGroup(group.getId());
-        System.out.println("DFGSDFGSDFGSDFG" + students.size());
         Assertions.assertEquals(students.size(), 2);
     }
 }

src/test/java/ru/IP_LabWorks/IP/SubjectServiceTests.java

@@ -5,16 +5,24 @@ import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
+import ru.IP_LabWorks.IP.University.Model.Group;
 import ru.IP_LabWorks.IP.University.Model.Subject;
+import ru.IP_LabWorks.IP.University.Service.GroupService;
 import ru.IP_LabWorks.IP.University.Service.SubjectService;
 
 import java.util.List;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 @SpringBootTest
 public class SubjectServiceTests {
     @Autowired
     private SubjectService subjectService;
 
+    @Autowired
+    private GroupService groupService;
+
     @Test
     void TestAddSubject(){
         subjectService.deleteAllSubjects();
@@ -28,7 +36,7 @@ public class SubjectServiceTests {
         final Subject subject = subjectService.addSubject("Философия");
 
         final Subject findSubject = subjectService.findSubject(subject.getId());
-        Assertions.assertEquals(subject, findSubject);
+        assertEquals(subject, findSubject);
     }
 
     @Test
@@ -38,7 +46,7 @@ public class SubjectServiceTests {
         final Subject subject2 = subjectService.addSubject("Математика");
 
         final List<Subject> subjects = subjectService.findAllSubjects();
-        Assertions.assertEquals(subjects.size(), 2);
+        assertEquals(subjects.size(), 2);
     }
 
     @Test
@@ -47,7 +55,7 @@ public class SubjectServiceTests {
         Subject subject = subjectService.addSubject("Философия");
 
         subject = subjectService.updateSubject(subject.getId(), "Математика");
-        Assertions.assertEquals(subject.getName(), "Математика");
+        assertEquals(subject.getName(), "Математика");
     }
 
     @Test
@@ -59,4 +67,39 @@ public class SubjectServiceTests {
             subjectService.findSubject(subject.getId());
         });
     }
+
+    @Test
+    void testAddAndFindGroupsInSubject() {
+        Subject subject = subjectService.addSubject("Math");
+        Group group1 = groupService.addGroup("PIBD-21");
+        Group group2 = groupService.addGroup("PIBD-22");
+
+        subjectService.addGroupToSubject(subject.getId(), group1.getId());
+        subjectService.addGroupToSubject(subject.getId(), group2.getId());
+
+        List<Group> groups = subjectService.findGroupsBySubject(subject.getId());
+
+        assertEquals(2, groups.size());
+        assertTrue(groups.contains(group1));
+        assertTrue(groups.contains(group2));
+    }
+
+    @Test
+    void testRemoveGroupFromSubject() {
+        Subject subject = subjectService.addSubject("Math");
+        Group group1 = groupService.addGroup("PIBD-21");
+        Group group2 = groupService.addGroup("PIBD-22");
+
+        subjectService.addGroupToSubject(subject.getId(), group1.getId());
+        subjectService.addGroupToSubject(subject.getId(), group2.getId());
+
+        List<Group> groupsBeforeRemove = subjectService.findGroupsBySubject(subject.getId());
+        assertEquals(2, groupsBeforeRemove.size());
+
+        subjectService.removeGroupFromSubject(subject.getId(), group1.getId());
+
+        List<Group> groupsAfterRemove = subjectService.findGroupsBySubject(subject.getId());
+        assertEquals(1, groupsAfterRemove.size());
+        assertTrue(groupsAfterRemove.contains(group2));
+    }
 }