MyBatis复杂映射开发之多对多查询

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：查询所有用户的同时查询出该用户对应的所有角色。

@startuml

!theme plain
top to bottom direction
skinparam linetype ortho

class sys_role {
   rolename: varchar(255)
   roleDesc: varchar(255)
   id: int(11)
}
class sys_user_role {
   userid: int(11)
   roleid: int(11)
}
class node2 as "user  /* 用户表 */" {
   username: varchar(50)
   password: varchar(50)
   birthday: varchar(50)
   id: int(11)
}

sys_user_role  ^-[#595959,plain]-  sys_role      : "roleid:id"
sys_user_role  ^-[#595959,plain]-  node2         : "userid:id"
@enduml

如果图片无法查看，请看这里

​

多对多查询的语句

对应的sql语句：

select u.id,u.username,r.id,r.rolename from user u left join sys_user_role ur on u.id=ur.userid
inner join sys_role r on r.id= ur.roleid

查询结果如下：

id	username	id	rolename
1	lucy	1	CTO
2	tom	1	CTO
1	lucy	2	CEO
2	tom	2	CEO

创建Role实体，修改User实体

User

class User {
    var id: Int? = null
    var username: String? = null

    // 代表当前用户具备那些订单
    var orderList: List<Order>? = null

    // 代表当前用户具备的那些角色
    var roleList: List<Role>? = null
    override fun toString(): String {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", orderList=" + orderList +
                ", roleList=" + roleList +
                '}'
    }
}

public class User {
    private Integer id;
    private String username;

    // 代表当前用户具备那些订单
    private List<Order> orderList;

    // 代表当前用户具备的那些角色
    private List<Role> roleList;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public List<Order> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }

    public List<Role> getRoleList() {
        return roleList;
    }

    public void setRoleList(List<Role> roleList) {
        this.roleList = roleList;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", orderList=" + orderList +
                ", roleList=" + roleList +
                '}';
    }
}

Role

class Role {
    private val id: Int? = null
    private val rolename: String? = null
  
    override fun toString(): String {
      return "Role{" +
      "id=" + id +
      ", rolename='" + rolename + '\'' +
      '}'
    }
}

public class Role {
    private Integer id;
    private String rolename;
  
  @Override
  public String toString() {
      return "Role{" +
              "id=" + id +
              ", rolename='" + rolename + '\'' +
              '}';
  }
}

UserMapper添加接口方法

/**
 * 查询所有用户以及对应的角色
 * @return
 */
fun findAllUserAndRole(): List<User?>?

/**
 * 查询所有用户以及对应的角色
 * @return
 */
public List<User> findAllUserAndRole();

配置UserMapper.xml

<resultMap id="userRoleMap" type="com.terwergreen.pojo.User">
    <result property="id" column="id"></result>
    <result property="username" column="username"></result>

    <collection property="roleList" ofType="com.terwergreen.pojo.Role">
        <result column="rid" property="id"></result>
        <result column="rolename" property="rolename"></result>
    </collection>
</resultMap>

<select id="findAllUserAndRole" resultMap="userRoleMap">
    select u.id,u.username,r.id,r.rolename from user u left join sys_user_role ur on u.id=ur.userid
    inner join sys_role r on r.id=ur.roleid
</select>

测试结果

==>  Preparing: select u.id,u.username,r.id as rid,r.rolename from user u left join sys_user_role ur on u.id=ur.userid inner join sys_role r on r.id=ur.roleid
==> Parameters: 
<==    Columns: id, username, rid, rolename
<==        Row: 1, lucy, 1, CTO
<==        Row: 2, tom, 1, CTO
<==        Row: 1, lucy, 2, CEO
<==        Row: 2, tom, 2, CEO
<==      Total: 4
User{id=1, username='lucy', orderList=null, roleList=[Role{id=1, rolename='CTO'}, Role{id=2, rolename='CEO'}]}
User{id=2, username='tom', orderList=null, roleList=[Role{id=1, rolename='CTO'}, Role{id=2, rolename='CEO'}]}

知识总结

MyBatis多表配置方式:

一对一配置:使用做配置

一对多配置:使用+做配置

多对多配置:使用+做配置

本文代码地址

mybatis-multitable

![NOTE]
文章更新历史

2022/05/08 feat:新增Kotlin支持。

2022/05/04 feat:初稿。