Spring Data JPA 写SQL语句也可以如此简单

    /**
     * 根据关注者id查找所有记录（查找关注的人的id）
     *
     * @param fromUserId
     * @return
     */
    @Query("select toUserId from Relationship where fromUserId =:fromUserId")
    List<Long> findByFromUserId(@Param("fromUserId") Long fromUserId);

SELECT DISTINCT t1.from_user_id FROM
(SELECT * FROM relationship WHERE to_user_id = 1)  AS t1
INNER JOIN relationship t2 ON t1.from_user_id = t2.to_user_id

@Query(value = "SELECT DISTINCT t1.to_user_id FROM (SELECT * FROM relationship WHERE from_user_id = ?1)  AS t1 INNER JOIN relationship t2 ON t1.to_user_id = t2.from_user_id ", nativeQuery = true)
List<Long> findFriendsByUserId(Long userId);

package com.liuyanzhao.forum.repository;

import com.liuyanzhao.forum.entity.Relationship;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;


/**
 * @author 言曌
 * @date 2018/4/24 下午9:56
 */

@SpringBootTest
@RunWith(SpringRunner.class)
public class RelationshipRepositoryTest {


    @Autowired
    private RelationshipRepository relationshipRepository;


    @Before
    public void save() {
        relationshipRepository.save(new Relationship(1L,2L));
        relationshipRepository.save(new Relationship(1L,3L));
        relationshipRepository.save(new Relationship(1L,4L));
        relationshipRepository.save(new Relationship(2L,1L));
        relationshipRepository.save(new Relationship(2L,4L));
        relationshipRepository.save(new Relationship(3L,1L));
    }



    @Test
    public void findFriendsByUserId() throws Exception {
        List<Long> ids = relationshipRepository.findFriendsByUserId(1L);
        System.out.println(ids);
    }

}

/**
  * 根据id集合查询用户
  *
  * @param ids
  * @return
  */
 List<User> findByIdIn(List<Long> ids);