Repository

package com.example.OepAchievers.Repository;

import com.example.OepAchievers.Model.Course;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.List;
@Repository
public interface CourseRepository extends JpaRepository<Course, Long> {
List<Course> findByInstructorId(Long instructorId);
List<Course> findByStatus(Course.CourseStatus status);
}

package com.example.OepAchievers.Repository;

import com.example.OepAchievers.Model.Enrollment;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.List;
@Repository
public interface EnrollmentRepository extends JpaRepository<Enrollment, Long> {
List<Enrollment> findByStudentId(Long studentId);
List<Enrollment> findByCourseId(Long courseId);
boolean existsByStudentIdAndCourseId(Long studentId, Long courseId);
}

package com.example.OepAchievers.Repository;

import com.example.OepAchievers.Model.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.Optional;
@Repository
public interface UserRepository extends JpaRepository<User, Long> {
Optional<User> findByUsername(String username);
boolean existsByEmail(String email);

}