Is 'jdbcType' necessary in a MyBatis resultMap?

Question

When we use Mybatis , in <select> ...</select> statment I know we need set jdbcType beacuse the IN variable maybe null, but when I see the document of Mybatis, I found jdbcType in <result>...</result> under ResultMap. the document of the jdbcTpe in <result>...</result> was:

... The JDBC type is only required for nullable columns upon insert, update or delete. This is a JDBC requirement, not a MyBatis one. So even if you were coding JDBC directly, you'd need to specify this type – but only for nullable values.

the bold word say only required for nullable columns upon insert, update or delete. BUT,the element of result is used in select neither insert, update or delete. so ,is it necessary use jdbcType in <result>...</result> ?

Answer 1

Most of the time, no. Why? Read on.

If you want to use a null as a JDBC parameter value you need to specify the jdbcType. That's a restriction of the JDBC specification you can't avoid. Therefore, if there's even a remote possibility a JDBC parameter could have a null value, then yes, specify it.

This does not apply to parameters preprocessed by MyBatis inside MyBatis tags, like the ones you use in the "test" attribute of the < if > tag. Those ones are not JDBC parameters.

Now, for the columns you read. These are the ones you are interested on. The thing is most of the time you don't need them. MyBatis will pick the right JDBC type for you. Well... this has been the case for me 99.999% of the time.

What about the other 0.001%? For some exotic column types -- that you rarely use -- MyBatis may pick the wrong JDBC type for you. The designers of MyBatis thought about this case, and give you the chance of overriding it. I think I remember an XML type database column that MyBatis was unsuccessfully trying to read as a VARCHAR, but I don't remember which database.

Bottom line, don't use it when reading columns, unless MyBatis reads exotic data type columns (XML, UUID, POINT, etc.) the wrong way.