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MyBatis关联映射之关联查询
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1 连接查询

在/src/main/java/cn.tedu.association.pojo目录下创建UserDetail.java文件：

@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class UserDetail {
    private User user;
    private Detail detail;
}

在/src/main/java/cn.tedu.association.dao/UserDao.java文件中添加：

public interface UserDao {
    ...
    public UserDetail getUserDetail(String username);
    ...
}

在/src/main/resources/mybatis-config.xml文件中添加：

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

在/src/main/resources/mappers/UserMapper.xml文件中添加：

<mapper namespace="cn.tedu.association.dao.UserDao">
    ...
    <!-- 连接查询 -->
    <resultMap id="userDetail" type="UserDetail">
        <result column="id" property="user.id" />
        <result column="usernane" property="user.username" />
        <result column="password" property="user.password" />
        <result column="realname" property="user.realname" />
        <result column="image" property="user.image" />
        <result column="detailid" property="detail.detailid" />
        <result column="address" property="detail.address" />
        <result column="telephone" property="detail.telephone" />
        <result column="description" property="detail.description" />
        <result column="userid" property="detail.userid" />
    </resultMap>
    <select id="getUserDetail" resultMap="userDetail">
        select id, username, password, realname, image, detailid, address, telephone, description, userid
        from t_user inner join t_detail on id = userid
        where username = #{username}
    </select>
    ...
</mapper>

在/src/test/java/cn/tedu/association/dao/UserDaoTest.java文件中添加：

public class UserDaoTest {
    ...
    @Test
    public void testGetUserDetail() {
        UserDao userDao = MyBatisUtil.getMapper(UserDao.class);
        UserDetail userDetail = userDao.getUserDetail("zhangfei");
        assertNotEquals(null, userDetail);
        System.out.println(userDetail);
    }
    ...
}

运行测试用例。

例程：Association

2 子查询

在/src/main/resources/mappers/UserMapper.xml文件中添加：

<mapper namespace="cn.tedu.association.dao.UserDao">
    ...
    <!-- 子查询 -->
    <resultMap id="userDetail" type="UserDetail">
        <result column="id" property="user.id" />
        <result column="usernane" property="user.username" />
        <result column="password" property="user.password" />
        <result column="realname" property="user.realname" />
        <result column="image" property="user.image" />
        <association column="id" property="detail"
                     select="cn.tedu.association.dao.DetailDao.getDetail" />
    </resultMap>
    <select id="getUserDetail" resultMap="userDetail">
        select id, username, password, realname, image from t_user
        where username = #{username}
    </select>
    ...
</mapper>

运行测试用例。

例程：Association