MyBatis vs MyBatis-Plus vs JPA：Java ORM 框架深度对比

// Mapper 接口
public interface UserMapper {
    @Select("SELECT * FROM user WHERE id = #{id}")
    User selectById(Long id);

    @Insert("INSERT INTO user(name, email) VALUES(#{name}, #{email})")
    int insert(User user);
}

<mapper namespace="com.example.mapper.UserMapper">
    <select id="selectById" resultType="User">
        SELECT * FROM user WHERE id = #{id}
    </select>
</mapper>

// 继承 BaseMapper，自动拥有 CRUD 方法
public interface UserMapper extends BaseMapper<User> {
    // 无需写任何方法，内置 insert、deleteById、
    // updateById、selectById 等 17+ 方法
}

// 使用
User user = userMapper.selectById(1L);
userMapper.insert(new User("Alice", "alice@example.com"));

// 继承 JpaRepository，自动拥有 CRUD
public interface UserRepository extends JpaRepository<User, Long> {
    // 方法名自动生成查询
    List<User> findByNameAndEmail(String name, String email);

    // 自定义 JPQL
    @Query("SELECT u FROM User u WHERE u.email LIKE %:domain")
    List<User> findByEmailDomain(@Param("domain") String domain);
}

<select id="findUsers" resultType="User">
    SELECT * FROM user
    <where>
        <if test="name != null">
            AND name LIKE CONCAT('%', #{name}, '%')
        </if>
        <if test="status != null">
            AND status = #{status}
        </if>
        <if test="startDate != null">
            AND create_time &gt;= #{startDate}
        </if>
    </where>
    ORDER BY create_time DESC
</select>

// LambdaQueryWrapper 类型安全，避免硬编码字段名
List<User> users = userMapper.selectList(
    new LambdaQueryWrapper<User>()
        .like(name != null, User::getName, name)
        .eq(status != null, User::getStatus, status)
        .ge(startDate != null, User::getCreateTime, startDate)
        .orderByDesc(User::getCreateTime)
);

// Spring Data JPA Specification
public class UserSpec {
    public static Specification<User> withFilters(
            String name, Integer status, LocalDateTime startDate) {
        return (root, query, cb) -> {
            List<Predicate> predicates = new ArrayList<>();
            if (name != null)
                predicates.add(cb.like(root.get("name"), "%" + name + "%"));
            if (status != null)
                predicates.add(cb.equal(root.get("status"), status));
            if (startDate != null)
                predicates.add(cb.greaterThanOrEqualTo(
                    root.get("createTime"), startDate));
            query.orderBy(cb.desc(root.get("createTime")));
            return cb.and(predicates.toArray(new Predicate[0]));
        };
    }
}

<select id="getUserWithOrders" resultMap="userOrderMap">
    SELECT u.*, o.id as order_id, o.amount
    FROM user u
    LEFT JOIN orders o ON u.id = o.user_id
    WHERE u.id = #{id}
</select>

@Entity
public class User {
    @Id
    private Long id;

    @OneToMany(mappedBy = "user", fetch = FetchType.LAZY)
    private List<Order> orders;
}

# MyBatis
mybatis:
  mapper-locations: classpath:mapper/*.xml
  type-aliases-package: com.example.entity

# MyBatis-Plus
mybatis-plus:
  mapper-locations: classpath:mapper/*.xml
  global-config:
    db-config:
      logic-delete-field: deleted
      logic-delete-value: 1
      logic-not-delete-value: 0

# JPA
spring:
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true
    properties:
      hibernate:
        format_sql: true

// 1. 使用 LambdaQueryWrapper 代替字符串字段名
// Bad
new QueryWrapper<User>().eq("name", "Alice");
// Good
new LambdaQueryWrapper<User>().eq(User::getName, "Alice");

// 2. 善用 Service 层封装
public interface UserService extends IService<User> {
    // 自定义业务方法
}

@Service
public class UserServiceImpl
    extends ServiceImpl<UserMapper, User>
    implements UserService {
    // IService 提供了 save、saveBatch、
    // getById、list、page 等便捷方法
}

// 3. 批量操作使用 saveBatch
userService.saveBatch(userList, 1000); // 每批 1000 条

// 1. 避免 N+1 问题：使用 EntityGraph
@EntityGraph(attributePaths = {"orders"})
List<User> findAll();

// 2. 只读查询使用投影（Projection）减少开销
public interface UserSummary {
    String getName();
    String getEmail();
}
List<UserSummary> findByStatus(Integer status);

// 3. 批量插入优化
spring.jpa.properties.hibernate.jdbc.batch_size=50
spring.jpa.properties.hibernate.order_inserts=true

<!-- 1. 使用 resultMap 复用映射 -->
<resultMap id="userMap" type="User">
    <id property="id" column="id"/>
    <result property="userName" column="user_name"/>
</resultMap>

<!-- 2. 使用 sql 片段复用 -->
<sql id="userColumns">
    id, user_name, email, status, create_time
</sql>

<select id="selectAll" resultMap="userMap">
    SELECT <include refid="userColumns"/>
    FROM user
</select>