[JAVA] ResultType behaves strangely in MyBatis Mapper XML

MyBatis did it again

Continued from last time, I heard that I was addicted to the strange movement of MyBatis again. That said, basically, I'm a little sloppy, and the one who made a mistake is a bad deal. I don't think MyBatis is bad (no, I think it's bad) Surprisingly, I can't find any mistakes myself and spend wasted time. I think it's rare, so I'll leave it so that if someone has a similar problem someday, I can solve it immediately.

The version of MyBatis is 3.2.

What happened

For some reason, the data held by Java's ʻIntegerdid not enter the DB'sNUMERIC` column. (I didn't get the error that was actually spit out, so I'll paste it later!) Certainly

** If you want to put String data in a NUMERIC column, explicitly CAST! ** **

I think it was an error content like that.

e? Why String? I have ʻInteger` ...? It is the content.

• The following source is a fucking code to convey the feeling. Variable names and method names are very suitable

ItemService.java

//Various omissions
...
...
...
List<Integer> itemMasterIds = itemMasterMapper.getIdsByCategoryName("tapioca");
//↓ ↓ An error occurs here ↓ ↓
userItemsMapper.add(user.getId(), itemMasterIds);

ItemMasterMapper.java

List<Integer> getIdsByCategoryName(@Param("categoryName") String categoryName);

ItemMasterMapper.xml

<select id="getIdsByCategoryName" resultType="string">
    SELECT item_master_id FROM item_master WHERE category = #{categoryName}
</select>

UserItemsMapper.java

void add(@Param("userId") long userId, @Param("itemMasterIds") List<Integer> itemMasterIds); 

UserItemsMapper.xml

<insert id="add">
    INSERT INTO user_items (user_id, item_master_id)
    VALUES
    <foreach collection="itemMasterIds" item="item" separator=",">
    (#{userId}, #{item})
    </foreach>
</insert>

Cause

Perhaps most people will find out instantly just by looking at the above code. ʻIn ItemMasterMapper.xml, set resultTypeofgetIdsByItemCategory, You wrote string`.

<select id="getIdsByItemCategory" resultType="string">

Normally, the return type defined in the Mapper interface and If the resultType defined in Mapper XML does not match, I think I'll get an error at that point, but for some reason ʻitem_master.item_master_id You can get it withList of String`, isn't it?

I can't find an error like this right away, or it's already the limit.