Mybatis多表查询

一对一查询

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

一对一查询的语句

对应的sql语句：

SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id;

查询的结果如下：

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;

}

创建OrderMapper接口

public interface OrderMapper {
    ListOrder> findAll();
}

配置OrderMapper.xml

mapper namespace="com.zjq.mapper.OrderMapper">
    resultMap id="orderMap" type="com.zjq.domain.Order">
        result column="uid" property="user.id">result>
        result column="username" property="user.username">result>
        result column="password" property="user.password">result>
        result column="birthday" property="user.birthday">result>
    resultMap>
    select id="findAll" resultMap="orderMap">
        SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id
    select>
mapper>

其中还可以配置如下：

resultMap id="orderMap" type="com.zjq.domain.Order">
    result property="id" column="id">result>
    result property="ordertime" column="ordertime">result>
    result property="total" column="total">result>
    association property="user" javaType="com.zjq.domain.User">
        result column="uid" property="id">result>
        result column="username" property="username">result>
        result column="password" property="password">result>
        result column="birthday" property="birthday">result>
    association>
resultMap>

测试结果

OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
ListOrder> all = mapper.findAll();
for(Order order : all){
    System.out.println(order);
}

输出：

一对多查询

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

一对多查询的语句

对应的sql语句：

select *,o.id oid from user u left join orders o on u.id=o.uid;

查询的结果如下：

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 ListOrder> orderList;
}

创建UserMapper接口

public interface UserMapper {
    ListUser> findAll();
}

配置UserMapper.xml

mapper namespace="com.zjq.mapper.UserMapper">
    resultMap id="userMap" type="com.zjq.domain.User">
        result column="id" property="id">result>
        result column="username" property="username">result>
        result column="password" property="password">result>
        result column="birthday" property="birthday">result>
        collection property="orderList" ofType="com.zjq.domain.Order">
            result column="oid" property="id">result>
            result column="ordertime" property="ordertime">result>
            result column="total" property="total">result>
        collection>
    resultMap>
    select id="findAll" resultMap="userMap">
        select *,o.id oid from user u left join orders o on u.id=o.uid
    select>
mapper>

测试结果

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
ListUser> all = mapper.findAll();
for(User user : all){
    System.out.println(user.getUsername());
    ListOrder> orderList = user.getOrderList();
    for(Order order : orderList){
        System.out.println(order);
    }
    System.out.println("----------------------------------");
}

输出：

15:00:24,330 DEBUG findAll:159 - ==>  Preparing: select u.id uid,u.username ,o.id oid,o.ordertime,o.total from user u left join orders o on u.id=o.uid 
15:00:24,360 DEBUG findAll:159 - ==> Parameters: 
15:00:24,393 DEBUG findAll:159 - =      Total: 5
User{id=1, username='admin', password='null', birthday=null, roleList=null, orderList=[Order{id=1, ordertime=Sun Apr 16 14:23:50 CST 2023, total=2000.0, user=null}]}
User{id=2, username='共饮一杯无666', password='null', birthday=null, roleList=null, orderList=[Order{id=2, ordertime=Sun Apr 16 14:23:50 CST 2023, total=8888.0, user=null}]}
User{id=3, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[Order{id=3, ordertime=Sun Apr 16 14:23:50 CST 2023, total=3699.0, user=null}]}
User{id=4, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[]}
User{id=5, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[]}

多对多查询

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

多对多查询的语句

对应的sql语句：

select u.*,r.*,r.id rid from user u left join sys_user_role ur on u.id=ur.userid

inner join sys_role r on ur.roleid=r.id;

查询的结果如下：

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 ListOrder> orderList;
    //代表当前用户具备哪些角色
    private ListRole> roleList;
}

public class Role {

    private int id;
    private String rolename;

}

添加UserMapper接口方法

ListUser> findAllUserAndRole();

配置UserMapper.xml

resultMap id="userRoleMap" type="com.zjq.domain.User">
    result column="id" property="id">result>
    result column="username" property="username">result>
    result column="password" property="password">result>
    result column="birthday" property="birthday">result>
    collection property="roleList" ofType="com.zjq.domain.Role">
        result column="rid" property="id">result>
        result column="rolename" property="rolename">result>
    collection>
resultMap>
select id="findAllUserAndRole" resultMap="userRoleMap">
    select u.*,r.*,r.id rid from user u left join sys_user_role ur on u.id=ur.userid
    inner join sys_role r on ur.roleid=r.id;
select>

测试结果

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

11:45:51,443 DEBUG findUserAndRoleAll:159 - ==>  Preparing: SELECT * FROM USER u,sys_user_role ur,sys_role r WHERE u.id=ur.userId AND ur.roleId=r.id 
11:45:51,572 DEBUG findUserAndRoleAll:159 - ==> Parameters: 
User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}
User{id=2, username='jack', password='123456', birthday=Fri Aug 20 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}
11:45:51,610 DEBUG findUserAndRoleAll:159 - =      Total: 4
11:45:51,618 DEBUG JdbcTransaction:123 - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:45:51,619 DEBUG JdbcTransaction:91 - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:45:51,619 DEBUG PooledDataSource:363 - Returned connection 1858609436 to pool.

Mybatis的注解开发

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

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 {
    ListUser> 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.zjq.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.zjq.mapper">package>
mappers>

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

一对一查询

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

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;

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;

}

创建OrderMapper接口

public interface OrderMapper {
    ListOrder> findAll();
}

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.zjq.mapper.UserMapper.findById"))
    })
    ListOrder> findAll();
}

public interface UserMapper {

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

测试结果

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

一对多查询

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

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;

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 ListOrder> orderList;
}

创建UserMapper接口

ListUser> findAllUserAndOrder();

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.zjq.mapper.OrderMapper.findByUid"))
    })
    ListUser> findAllUserAndOrder();
}

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

}

测试结果

ListUser> all = userMapper.findAllUserAndOrder();
for(User user : all){
    System.out.println(user.getUsername());
    ListOrder> orderList = user.getOrderList();
    for(Order order : orderList){
        System.out.println(order);
    }
    System.out.println("-----------------------------");
}

多对多查询

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

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

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 ListOrder> orderList;
    //代表当前用户具备哪些角色
    private ListRole> roleList;
}

public class Role {

    private int id;
    private String rolename;

}

添加UserMapper接口方法

ListUser> findAllUserAndRole();

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.zjq.mapper.RoleMapper.findByUid"))
})
ListUser> findAllUserAndRole();}



public interface RoleMapper {
    @Select("select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=#{uid}")
    ListRole> findByUid(int uid);
}

测试结果

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

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