Optimize student queries with QueryDSL to reduce N+1 queries

[Copilot]

Student lookup operations were executing multiple separate queries (N+1 problem), fetching user, student info, fixed rooms, and attendance data in separate database round trips.

Changes

• Added StudentQueryRepository with QueryDSL methods that fetch all student data in single queries using joins:

  • findAllInfoByStatusAndRoomAndType() - fetch by room and attendance type
  • findAllInfoByStatusAndGradeAndCls() - fetch by grade and class
  • findAllInfoByRoomTypeStatusAndRole() - fetch by room type and status

• Refactored service layer to use new repository methods:

  • GetStudentService now calls findAllInfoByStatusAndRoomAndType() and findAllInfoByStatusAndGradeAndCls()
  • GetNotAttendedStudentService leverages same methods with status filtering

Query Example

Before: Multiple queries executed per student

// Separate queries for each entity
students.forEach { student ->
    studentInfo = findStudentInfo(student.id)
    fixedRooms = findFixedRooms(student.id)
    attendance = findAttendance(student.id)
}

After: Single query with joins

queryFactory.from(userEntity)
    .innerJoin(studentInfoEntity).on(...)
    .innerJoin(fixedRoomEntity).on(...)
    .leftJoin(attendanceEntity).on(...)
    .transform(groupBy(userEntity.id).list(...))

The new queries use groupBy with transform() to aggregate related entities and return a List<StudentQueryDto> containing all necessary data from a single database query.

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