partial repeated data leads to result data loss

[pop1213]

MyBatis version

3.5.15

Database vendor and version

mysql8

Test case or example project

Steps to reproduce

create table and import data

create table if not exists tb_user
(
    user_name varchar(100) null,
    user_id   int          null,
    password  varchar(100) null
);
create table tb_other
(
    col1 varchar(20) null,
    col2 varchar(20) null,
    col3 int         null
);

INSERT INTO tb_user (user_name, user_id, password) VALUES ('test', 1, '1');

INSERT INTO tb_other (col1, col2, col3) VALUES ('test', 'xxx', 1);
INSERT INTO tb_other (col1, col2, col3) VALUES ('test', 'xxx', 2);

mapper.xml

    <resultMap id="testMap" type="com.cyb.admin.domain.TbUser">
        <id property="userId" column="user_id"/>
        <id property="userName" column="user_name"/>

<!--        <collection property="dictTags" ofType="java.lang.String"></collection>-->
        <collection property="others" ofType="com.cyb.admin.domain.TbOther">
            <result column="col1" property="col1"></result>
            <result column="col2" property="col2"></result>
      </collection>
    </resultMap>

    <select id="selectTest" parameterType="int" resultMap="testMap" resultOrdered="true">
        select t1.user_id, t1.user_name, t2.col1, t2.col2
        from tb_user t1
                 left join tb_other t2 on t1.user_name = t2.col1
    </select>

entity Class

@NoArgsConstructor
@Data
public class TbUser {
    private String userName;
    private Long userId;

    List<TbOther> others;
}

@NoArgsConstructor
@Data
public class TbOther {
    private String col1;
    private String col2;
}

execute sql , result like this

test code

    MybatisTestMapper mapper = sqlSession.getMapper(MybatisTestMapper.class);

    List<TbUser> list = mapper.selectTest();
    System.out.println("list size:"+list.size());
    System.out.println("list.others size:"+list.get(0).getOthers().size());

Expected result

list size:1
list.others size:2

Actual result

list size:1
list.others size:1

[harawata]

Hello @pop1213 ,

That is the expected behavior because, in the <collection />, there is no <id> element and the values of col1 and col2 are the same.

If the value of col3 is unique for each row of tb_other, you can use it as ID.

<collection property="others" ofType="com.cyb.admin.domain.TbOther">
  <id column="col3" />
  <result column="col1" property="col1" />
  <result column="col2" property="col2" />
</collection>

[pop1213]

I understand what you mean. However, in the above scenario, the console log printing shows that there are two pieces of data, but I get no result at all. This may be puzzling.

[harawata]

@pop1213 ,

I am not sure what you mean. If you need further assistance, please create a small repro project like these and share it on your GitHub repository. We may be able to understand what you expect by taking a look at the assertions in the test case.