Mybatis的注解开发

一、Mybatis的注解开发

1.1 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

1.2 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>
    
    <mapper class="com.itheima.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>
    
    <package name="com.itheima.mapper">package>
mappers>

1.3 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
Mybatis的注解开发_第1张图片

Mybatis的注解开发_第2张图片

2.一对一查询

2.1 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

Mybatis的注解开发_第3张图片

2.2 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uid;

查询的结果如下:

Mybatis的注解开发_第4张图片

2.3 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;

}
2.4 创建OrderMapper接口
public interface OrderMapper {
    List<Order> findAll();
}
2.5 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.itheima.mapper.UserMapper.findById"))
    })
    List<Order> findAll();
}
public interface UserMapper {

    @Select("select * from user where id=#{id}")
    User findById(int id);
    
}
2.6 测试结果
@Test
public void testSelectOrderAndUser() {
    List<Order> all = orderMapper.findAll();
    for(Order order : all){
        System.out.println(order);
    }
}

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-XxbAH5F1-1653360939282)(img\图片14.png)]

3. 一对多查询

3.1 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

Mybatis的注解开发_第5张图片

3.2 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id;

查询的结果如下:

Mybatis的注解开发_第6张图片

3.3 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;
}
3.4 创建UserMapper接口
List<User> findAllUserAndOrder();
3.5 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.itheima.mapper.OrderMapper.findByUid"))
    })
    List<User> findAllUserAndOrder();
}

public interface OrderMapper {
    @Select("select * from orders where uid=#{uid}")
    List<Order> findByUid(int uid);

}
3.6 测试结果
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("-----------------------------");
}

Mybatis的注解开发_第7张图片

4.多对多查询

4.1 多对多查询的模型

用户表和角色表的关系为,一个用户有多个角色,一个角色被多个用户使用

多对多查询的需求:查询用户同时查询出该用户的所有角色

Mybatis的注解开发_第8张图片

4.2 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:

Mybatis的注解开发_第9张图片

4.3 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角色
    private List<Role> roleList;
}

public class Role {

    private int id;
    private String rolename;

}
4.4 添加UserMapper接口方法
List<User> findAllUserAndRole();
4.5 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.itheima.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);
}

4.6 测试结果
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("----------------------------------");
}

Mybatis的注解开发_第10张图片

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