Mybatis is a data mapping framework I recently came across. I did step by step tutorials like getting-started-with-ibatis-mybatis-annotations and mybatis-dao-example-code-tutorial .
These tutorials show as well as others how to map database columns to java class members, e.g.
@Results(value = {
@Result(property="ID", column="ID"),
@Result(property="column_one", column="column_one"),
@Result(property="column_B", column="column_B")
})
Seeing this kind of mapping often – I wondered if the mapping is really necessary?
I realized you don’t need to define an explicit mapping in any case. According to the mybatis configuration settings and some tests I did, you need to make sure 2 details are set:
- java class members and database columns uses the same labels
- mybatis mapping config file setting autoMappingBehavior is ist set to PARTIAL or FULL
<setting name="autoMappingBehavior" value="FULL"/>
In cases like this you can leave the mapping empty e.g.
@Select(SELECTALL)
// @Results(value = {
// @Result(property="ID", column="ID"),
// @Result(property="column_one", column="column_one"),
// @Result(property="column_B", column="column_B")
// })
List selectAll();
On the other hand you are required to define the mapping in some situations .
If there are different labels for java properties and database columns and/or you tell mybatis not to automatically map, you have to define a mapping.
A mapping definition could look like this:
@Select(SELECTALL)
@Results(value = {
@Result(property="ID", column="ID"),
@Result(property="column_one", column="column_one"),
@Result(property="prop2", column="column_B")
})
List selectAll();
A match to your java class members
private int ID;
private String prop2;
private int column_one;
and your database table definitions e.g.
CREATE TABLE things(
ID INT NOT NULL AUTO_INCREMENT,
column_one INT NOT NULL,
column_B VARCHAR(60) NOT NULL,
);
is required in order to complete the sample.
If you want to know more about the sample code snippets, you can check out a sample code project mybatisMappingTest on github. This project consists of two branches:
The branch explicitMapping shows by example how to define an explicit mapping. How mybatis maps data automatically is shown in branch autoMapping .
