Use of annotations @mapkey in MyBatis

Before studying the MyBatis source code is not aware of the magic of this note, but when I see the parameter parsing there is an annotation, so I understand a bit, when we return like Map<string, Map<string, object>> This type of time, we are often difficult to do, because the surface may be more than one table of data, so we can not build a model.

That's when we can use this annotation.

@Retention (retentionpolicy.runtime) @Target (elementtype.method) public @interface Mapkey {  String value ();}

Obviously, this annotation is a function of the method, the specific use is to set the external map of the key is what. This allows us to query for very complex results without having to create a new entity

Use of annotations @mapkey in MyBatis