mybatis学习第六部分：Mybatis注解开发

6.1   MyBatis的常⽤注解

这⼏年来注解开发越来越流⾏，Mybatis也可以使⽤注解开发⽅式，这样我们就可以减少编写Mapper

映射⽂件了。我们先围绕⼀些基本的CRUD来学习，再学习复杂映射多表操作。

@Insert：实现新增

@Update：实现更新

@Delete：实现删除

@Select：实现查询

@Result：实现结果集封装

@Results：可以与@Result    ⼀起使⽤，封装多个结果集

@One：实现⼀对⼀结果集封装

@Many：实现⼀对多结果集封装

 

6.2   MyBatis的增删改查

我们完成简单的user表的增删改查的操作

private UserMapper userMapper;
@Before
public void before() throws IOException {
InputStream resourceAsStream =
Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new
SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
userMapper = sqlSession.getMapper(UserMapper.class);
}
@Test
public void testAdd() {
User user = new User();
user.setUsername("测试数据");
user.setPassword("123");
user.setBirthday(new Date());
userMapper.add(user);
}
@Test
public void testUpdate() throws IOException {
User user = new User();
user.setId(16);
user.setUsername("测试数据修改");
user.setPassword("abc");
user.setBirthday(new Date());
userMapper.update(user);
}
@Test
public void testDelete() throws IOException {
userMapper.delete(16);
}
@Test
public void testFindById() throws IOException {
User user = userMapper.findById(1);
System.out.println(user);
}
@Test
public void testFindAll() throws IOException {
List<User> all = userMapper.findAll();
for(User user : all){
System.out.println(user);
}
}

修改MyBatis的核⼼配置⽂件，我们使⽤了注解替代的映射⽂件，所以我们只需要加载使⽤了注解的

Mapper接⼝即可

<mappers>
    <!--扫描使⽤注解的类-->
    <mapper class="com.lagou.mapper.UserMapper"></mapper>
</mappers>

或者指定扫描包含映射关系的接⼝所在的包也可以

<mappers>
    <!--扫描使⽤注解的类所在的包-->
    <package name="com.lagou.mapper"></package>
</mappers>

6.3 MyBatis的注解实现复杂映射开发

实现复杂关系映射之前我们可以在映射⽂件中通过配置来实现，使⽤注解开发后，我们可以使⽤

@Results注解，@Result注解，@One注解，@Many注解组合完成复杂关系的配置

6.4 ⼀对⼀查询

6.4.1 ⼀对⼀查询的模型

⽤户表和订单表的关系为，⼀个⽤户有多个订单，⼀个订单只从属于⼀个⽤户

⼀对⼀查询的需求：查询⼀个订单，与此同时查询出该订单所属的⽤户

6.4.2 ⼀对⼀查询的语句

对应的sql语句：

select * from orders;

select * from user where id=查询出订单的ID

查询的结果如下：

6.4.3  创建Order和User实体

public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单从属于哪⼀个客户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
}

6.4.4  创建OrderMapper接⼝

public interface OrderMapper {
    List<Order> findAll();
}

6.4.5  使⽤注解配置Mapper

public interface OrderMapper {
@Select("select * from orders")
@Results({
@Result(id=true,property = "id",column = "id"),
@Result(property = "ordertime",column = "ordertime"),
@Result(property = "total",column = "total"),
@Result(property = "user",column = "uid", javaType = User.class,
one = @One(select = "com.lagou.mapper.UserMapper.findById"))
})
List<Order> findAll();
}

public interface UserMapper {
@Select("select * from user where id=#{id}")
User findById(int id);
}

6.4.6 测试代码

@Test
public void testSelectOrderAndUser() {
List<Order> all = orderMapper.findAll();
for(Order order : all){
System.out.println(order);
}
}

6.4.7 测试结果

6.5 ⼀对多查询

6.5.1 ⼀对多查询的模型

⽤户表和订单表的关系为，⼀个⽤户有多个订单，⼀个订单只从属于⼀个⽤户

⼀对多查询的需求：查询⼀个⽤户，与此同时查询出该⽤户具有的订单

6.5.2 ⼀对多查询的语句

对应的sql语句：

select * from user;

select * from orders where uid=查询出⽤户的

查询的结果如下：

6.5.3  修改User实体

public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单从属于哪⼀个客户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表当前⽤户具备哪些订单
private List<Order> orderList;
}

6.5.4  创建UserMapper接⼝：

List<User> findAllUserAndOrder();

6.5.5  使⽤注解配置Mapper

public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id = true,property = "id",column = "id"),
@Result(property = "username",column = "username"),
@Result(property = "password",column = "password"),
@Result(property = "birthday",column = "birthday"),
@Result(property = "orderList",column = "id",
javaType = List.class,
many = @Many(select =
"com.lagou.mapper.OrderMapper.findByUid"))
})
List<User> findAllUserAndOrder();
}
public interface OrderMapper {
@Select("select * from orders where uid=#{uid}")
List<Order> findByUid(int uid);
}

6.5.6 测试代码

List<User> all = userMapper.findAllUserAndOrder(); 
for(User user : all){
System.out.println(user.getUsername()); 
List<Order> orderList = user.getOrderList(); 

for(Order order : orderList){
System.out.println(order);
}
System.out.println("-----------------------------");
}

6.5.7测试结果：

 

6.6 多对多查询

6.6.1 多对多查询的模型

⽤户表和⻆⾊表的关系为，⼀个⽤户有多个⻆⾊，⼀个⻆⾊被多个⽤户使⽤ 多对多查询的需求：查询⽤户同时查询出该⽤户的所有⻆⾊

6.6.2 多对多查询的语句

对应的sql语句：

 

select * from user;
select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=⽤户的id

查询的结果如下：

6.6.3  创建Role实体，修改User实体

public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表当前⽤户具备哪些订单
private List<Order> orderList;
//代表当前⽤户具备哪些⻆⾊
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}

6.6.4  添加UserMapper接⼝⽅法

List<User> findAllUserAndRole();

6.6.5  使⽤注解配置Mapper

public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id = true,property = "id",column = "id"),
@Result(property = "username",column = "username"),
@Result(property = "password",column = "password"),
@Result(property = "birthday",column = "birthday"),
@Result(property = "roleList",column = "id",
javaType = List.class,
many = @Many(select =
"com.lagou.mapper.RoleMapper.findByUid"))
})
List<User> findAllUserAndRole();}
public interface RoleMapper {
@Select("select * from role r,user_role ur where r.id=ur.role_id and
ur.user_id=#{uid}")
List<Role> findByUid(int uid);
}

6.6.6 测试代码：

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){
System.out.println(user.getUsername());
List<Role> roleList = user.getRoleList();
for(Role role : roleList){
System.out.println(role);
}
System.out.println("----------------------------------");
}

6.6.7 测试结果