backend/src/main/java/nju/seec/helper/dao/ChooseDAO.java

package nju.seec.helper.dao;

import nju.seec.helper.entity.Choose;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

import java.util.Optional;
import java.util.Set;

/**
 * @author cst
 */
@Repository
public interface ChooseDAO extends JpaRepository<Choose, Integer> {
    /**
     * 检查学生的选课信息是否存在
     *
     * @param studentId
     * @param courseId
     * @return
     */
    boolean existsByStudentIdAndCourseId(Integer studentId, Integer courseId);

    /**
     * 查询选课信息
     *
     * @param studentId
     * @param courseId
     * @return
     */
    Optional<Choose> findByStudentIdAndCourseId(Integer studentId, Integer courseId);

    /**
     * 查询学生选课信息
     *
     * @param studentId
     * @return
     */
    @Query("select distinct choose.courseId from Choose choose where choose.studentId=?1")
    Set<Integer> findCourseIdsByStudentId(Integer studentId);

    /**
     * 查询课程的选课学生
     *
     * @param courseId
     * @return
     */
    @Query("select distinct c.studentId from Choose c where c.courseId=?1")
    Set<Integer> findStudentIdsByCourseId(Integer courseId);
}