How to reuse MyBatis's mapper in another mapper?

Question

I have tables event and message , which have one-to-one relationship and are represented by classes:

public class Event {
    private Long id;
    private Message message;
}

public class Message {
    private Long id;
}

And there are two mappers: EventMapper and MessageMapper :

public interface EventMapper {

    @Select("SELECT * FROM event WHERE date BETWEEN #{from} AND #{to}")
    @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "message", column = "message_id",
                    javaType = Message.class, one = @One(select = "getMessage"))
    })
    List<Event> selectInInterval(@Param("from") Date from, @Param("to") Date to);

    @Select("SELECT * FROM message WHERE id = #{id}")
    Message getMessage(@Param("id") Long id);
}


public interface MessageMapper {

    @Select("SELECT * FROM message WHERE id = #{id}")
    @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "text", column = "text")
    })
    List<Event> selectById(@Param("id") Long id);
}

EventMapper selects events and maps them via an annotation, using getMessage to select and map event's message. But I already have identical method selectById in MessageMapper , so is it possible to reuse it?

Answer 1

In order to use any definition from the other mapper including a statement or ResultMap you should include namespace (fully qualified name) of the mapper into the identifier of that entity.

In your example assuming that MessageMapper is in com.company.app.mappers package it would be:

public interface EventMapper {

    @Select("SELECT * FROM event WHERE date BETWEEN #{from} AND #{to}")
    @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "message", column = "message_id",
                    javaType = Message.class,
                    one = @One(select = "com.company.app.mappers.MessageMapper.getMessage"))
    })
    List<Event> selectInInterval(@Param("from") Date from, @Param("to") Date to);
}