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MyBatis关联映射之多一关联
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员工->部门

1 连接查询

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class EmployeeDepartment {
    private Employee employee;
    private Department department;
}

public interface EmployeeDao {
    ...
    public EmployeeDepartment getEmployeeDepartment(String number);
    ...
}

<typeAliases>
    ...
    <typeAlias type="cn.tedu.association.pojo.EmployeeDepartment" alias="EmployeeDepartment" />
    ...
</typeAliases>

<mapper namespace="cn.tedu.association.dao.EmployeeDao">
    ...
    <!-- 连接查询 -->
    <resultMap id="employeeDepartment" type="EmployeeDepartment">
        <result column="number" property="employee.number" />
        <result column="fullname" property="employee.fullname" />
        <result column="age" property="employee.age" />
        <result column="department" property="employee.department" />
        <result column="id" property="department.id" />
        <result column="name" property="department.name" />
        <result column="description" property="department.description" />
    </resultMap>
    <select id="getEmployeeDepartment" resultMap="employeeDepartment">
        select number, fullname, age, department, id, name, description
        from t_employee inner join t_department on department = id
        where number = #{number}
    </select>
    ...
</mapper>

public class EmployeeDaoTest {
    @Test
    public void testGetEmployeeDepartment() {
        EmployeeDao employeeDao = MyBatisUtil.getMapper(EmployeeDao.class);
        EmployeeDepartment employeeDepartment = employeeDao.getEmployeeDepartment("1001");
        assertNotEquals(null, employeeDepartment);
        System.out.println(employeeDepartment);
    }
}

运行测试用例。

例程：Association

2 子查询

public interface DepartmentDao {
    ...
    public Department getDepartment(int id);
    ...
}

<mapper namespace="cn.tedu.association.dao.DepartmentDao">
    ...
    <select id="getDepartment" resultType="Department">
        select id, name, description from t_department
        where id = #{id}
    </select>
    ...
</mapper>

<mapper namespace="cn.tedu.association.dao.EmployeeDao">
    ...
    <!-- 子查询 -->
    <resultMap id="employeeDepartment" type="EmployeeDepartment">
        <result column="number" property="employee.number" />
        <result column="fullname" property="employee.fullname" />
        <result column="age" property="employee.age" />
        <result column="department" property="employee.department" />
        <association column="department" property="department"
                     select="cn.tedu.association.dao.DepartmentDao.getDepartment" />
    </resultMap>
    <select id="getEmployeeDepartment" resultMap="employeeDepartment">
        select number, fullname, age, department from t_employee
        where number = #{number}
    </select>
    ...
</mapper>

运行测试用例。

例程：Association