MyBatis笔记——多对一映射问题解决

<select id="getEmpAndDept" resultMap="empAndDeptResultMapTwo">  
    select * from t_emp 
    left join t_dept on t_emp.did = t_dept.did    
    where t_emp.eid = #{eid}
select>
1
2
3
4
5

@Data  
@AllArgsConstructor  
@NoArgsConstructor  
public class Emp {  
    private Integer eid;  
    private String empName;  
    private Integer age;  
    private String sex;  
    private String email;  
    private Dept dept;  
}
1
2
3
4
5
6
7
8
9
10
11

@Data  
@AllArgsConstructor  
@NoArgsConstructor  
public class Dept {  
    private Integer did;  
    private String deptName;  
}
1
2
3
4
5
6
7

<resultMap id="empAndDeptResultMapOne" type="Emp">  
      
    <id property="eid" column="eid"/>  
    <result property="empName" column="emp_name"/>  
    <result property="age" column="age"/>  
    <result property="sex" column="sex"/>  
    <result property="email" column="email"/>  
    <result property="dept.did" column="did"/>  
    <result property="dept.deptName" column="dept_name"/>  

<resultMap id="empAndDeptResultMapOne" type="Emp">  
      
    <id property="eid" column="eid"/>  
    <result property="empName" column="emp_name"/>  
    <result property="age" column="age"/>  
    <result property="sex" column="sex"/>  
    <result property="email" column="email"/>  
    <result property="dept.did" column="did"/>  
    <result property="dept.deptName" column="dept_name"/>  

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10

使用 解决

<resultMap id="empAndDeptResultMapTwo" type="Emp">  
      
    <id property="eid" column="eid"/>  
    <result property="empName" column="emp_name"/>  
    <result property="age" column="age"/>  
    <result property="sex" column="sex"/>  
    <result property="email" column="email"/>  
    <association property="dept" javaType="dept">  
        <id property="did" column="did"/>  
        <result property="deptName" column="dept_name"/>  
    association>  
resultMap>
1
2
3
4
5
6
7
8
9
10
11
12

分布查询 解决

1. 分别在两个表对应的mapper，使用能关联的字段进行查询

Emp getEmpAndDeptByStepOne(Integer eid);
1

<select id="getEmpAndDeptByStepOne">  
    select *  
    from t_emp             
    left join t_dept on t_emp.did = t_dept.did    
    where t_emp.eid = #{eid}
select>
1
2
3
4
5
6

Dept getEmpAndDeptByStepTwo(Integer did);
1

<select id="getEmpAndDeptByStepTwo" resultType="com.zxb.mybatis.pojo.Dept">  
    select * from t_dept where did = #{did}  
select>
1
2
3

2. 在主表的映射文件中，添加字段，并用该字段查询子表

<resultMap id="empAndDeptByStepResultMap" type="Emp">  
      
    <id property="eid" column="eid"/>  
    <result property="empName" column="emp_name"/>  
    <result property="age" column="age"/>  
    <result property="sex" column="sex"/>  
    <result property="email" column="email"/>  
    <association property="dept" select="com.zxb.mybatis.mapper.DeptMapper.getEmpAndDeptByStepTwo" column="did"/>  
resultMap>
1
2
3
4
5
6
7
8
9

<select id="getEmpAndDeptByStepOne" resultMap="empAndDeptByStepResultMap">  
    select *  
    from t_emp             
    left join t_dept on t_emp.did = t_dept.did    
    where t_emp.eid = #{eid}
select>
1
2
3
4
5
6