SpringData JPA与MyBatis对比

MyBatis 把 SQL 的控制权交给开发者，这是它的优点也是它的难点。动态 SQL、缓存机制、参数处理都是需要掌握的知识点。本文讲实际项目中的使用经验和优化技巧。

设计理念对比

特性	JPA	MyBatis
设计思想	ORM（对象关系映射）	SQL Mapping（SQL映射）
SQL 控制	自动生成	手动编写
学习曲线	较陡	平缓
灵活性	较低	高
性能调优	较难	容易
复杂查询	较麻烦	方便
数据库迁移	容易	较麻烦
缓存	内置二级缓存	需手动配置

JPA 示例

实体定义

@Entity
@Table(name = "t_user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @Column(name = "user_name", nullable = false, length = 50)
    private String username;
    
    @Column(name = "email")
    private String email;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "dept_id")
    private Department department;
    
    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
    private List<Order> orders;
}

Repository

public interface UserRepository extends JpaRepository<User, Long> {
    
    // 方法名解析查询
    List<User> findByUsernameContainingAndStatus(String username, Integer status);
    
    // JPQL
    @Query("SELECT u FROM User u WHERE u.department.name = :deptName")
    List<User> findByDepartmentName(@Param("deptName") String deptName);
    
    // 原生 SQL
    @Query(value = "SELECT * FROM t_user WHERE create_time > ?1", nativeQuery = true)
    List<User> findRecentUsers(LocalDateTime date);
    
    // 分页
    Page<User> findByStatus(Integer status, Pageable pageable);
    
    // 更新
    @Modifying
    @Query("UPDATE User u SET u.status = ?1 WHERE u.id = ?2")
    int updateStatus(Integer status, Long id);
}

使用

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;
    
    public User getUser(Long id) {
        return userRepository.findById(id).orElse(null);
    }
    
    public Page<User> listUsers(int page, int size) {
        return userRepository.findByStatus(1, PageRequest.of(page, size));
    }
}

MyBatis 示例

Mapper XML

<!-- UserMapper.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.example.mapper.UserMapper">
    
    <resultMap id="userResultMap" type="com.example.entity.User">
        <id property="id" column="id"/>
        <result property="username" column="user_name"/>
        <result property="email" column="email"/>
        <association property="department" javaType="Department">
            <id property="id" column="dept_id"/>
            <result property="name" column="dept_name"/>
        </association>
    </resultMap>
    
    <select id="selectById" resultMap="userResultMap">
        SELECT u.*, d.name as dept_name
        FROM t_user u
        LEFT JOIN t_department d ON u.dept_id = d.id
        WHERE u.id = #{id}
    </select>
    
    <select id="selectByCondition" resultMap="userResultMap">
        SELECT u.*, d.name as dept_name
        FROM t_user u
        LEFT JOIN t_department d ON u.dept_id = d.id
        <where>
            <if test="username != null">
                AND u.user_name LIKE CONCAT('%', #{username}, '%')
            </if>
            <if test="status != null">
                AND u.status = #{status}
            </if>
        </where>
        ORDER BY u.create_time DESC
    </select>
    
    <insert id="insert" useGeneratedKeys="true" keyProperty="id">
        INSERT INTO t_user (user_name, email, status)
        VALUES (#{username}, #{email}, #{status})
    </insert>
    
    <update id="update">
        UPDATE t_user
        <set>
            <if test="username != null">user_name = #{username},</if>
            <if test="email != null">email = #{email},</if>
        </set>
        WHERE id = #{id}
    </update>
</mapper>

Mapper 接口

@Mapper
public interface UserMapper {
    User selectById(Long id);
    List<User> selectByCondition(@Param("username") String username, 
                                  @Param("status") Integer status);
    int insert(User user);
    int update(User user);
}

使用

@Service
public class UserService {
    @Autowired
    private UserMapper userMapper;
    
    public User getUser(Long id) {
        return userMapper.selectById(id);
    }
    
    public List<User> searchUsers(String username, Integer status) {
        return userMapper.selectByCondition(username, status);
    }
}

MyBatis-Plus（增强）

@Mapper
public interface UserMapper extends BaseMapper<User> {
}

@Service
public class UserService extends ServiceImpl<UserMapper, User> {
    
    public List<User> getActiveUsers() {
        return lambdaQuery()
            .eq(User::getStatus, 1)
            .like(StringUtils.isNotBlank(name), User::getUsername, name)
            .list();
    }
    
    public IPage<User> getUserPage(int current, int size) {
        return page(new Page<>(current, size),
            new QueryWrapper<User>().orderByDesc("create_time"));
    }
}

选型建议

场景	推荐
快速开发、CRUD 为主	JPA / MyBatis-Plus
复杂 SQL、性能敏感	MyBatis
多表关联、对象关系复杂	JPA
遗留系统、SQL 已存在	MyBatis
团队熟悉 SQL	MyBatis
团队熟悉 Hibernate	JPA
需要数据库无关性	JPA

混合使用

@Service
public class OrderService {
    
    @Autowired
    private OrderRepository orderRepository;  // JPA
    
    @Autowired
    private ReportMapper reportMapper;        // MyBatis
    
    public Order getOrder(Long id) {
        return orderRepository.findById(id).orElse(null);
    }
    
    public List<Map<String, Object>> getReport() {
        return reportMapper.selectComplexReport();
    }
}