[FEATURE] 학과 조회 API 최적화 (#155)

* feat: member_count 필드 추가 (#154)

* feat: 학과 조회 API 수정 (#154)

* feat: 회원가입 시 데이터 동기화 (#154)

* feat: 회원 탈퇴 시 데이터 동기화 (#154)

src/main/java/com/smunity/server/domain/department/dto/DepartmentResponseDto.java

@@ -27,7 +27,7 @@ private static DepartmentResponseDto from(Department department) {
                 .college(department.getCollege())
                 .name(department.getName())
                 .code(department.getCode())
-                .count(department.getMembers().size())
+                .count(department.getMemberCount())
                 .build();
     }
 }

src/main/java/com/smunity/server/domain/member/service/MemberCommandService.java

@@ -60,6 +60,6 @@ public MemberInfoResponseDto changePasswordByAuth(String username, ChangePasswor
 
     public void deleteMember(Long memberId) {
         Member member = memberRepository.findById(memberId).orElseThrow(() -> new GeneralException(ErrorCode.MEMBER_NOT_FOUND));
-        memberRepository.delete(member);
+        member.delete();
     }
 }

src/main/java/com/smunity/server/global/common/entity/Department.java

@@ -30,8 +30,15 @@ public class Department {
     @Column(nullable = false)
     private boolean isEditable;
 
+    @Column(nullable = false)
+    private int memberCount = 0;
+
     private String code;
 
     @OneToMany(mappedBy = "department", cascade = CascadeType.ALL, orphanRemoval = true)
     private final List<Member> members = new ArrayList<>();
+
+    public void updateMemberCount() {
+        this.memberCount = members.size();
+    }
 }

src/main/java/com/smunity/server/global/common/entity/Member.java

@@ -67,6 +67,7 @@ public class Member extends BaseEntity {
     public void setDepartment(Department department) {
         this.department = department;
         department.getMembers().add(this);
+        department.updateMemberCount();
     }
 
     public void setInfo(Year year, Department department, String encodePw) {
@@ -81,6 +82,13 @@ public void update(Department department, String name, String email) {
         this.email = email;
     }
 
+    public void delete() {
+        Department department = this.department;
+        this.department = null;
+        department.getMembers().remove(this);
+        department.updateMemberCount();
+    }
+
     public void changePassword(String password) {
         this.password = password;
     }