The Challenge of the ORM in Java(Simple querying)

@DomainModel
public class Blog {
    private Long id;
    private String title;
    private Integer state;

    @Relation(relationType = RelationType.BELONGS_TO)
    private Author author;
}

<mapper>
  <resultMap type="Blog" id="blog">
    <id column="id" property="id" />
    ...
    <association property="author" javaType="Author">
      ...
    </association>
  </resultMap>
  <select id="findBlog" parameterType="int" resultMap="blog">
    ...
  </select>
</mapper>

...
BlogMapper mapper = session.getMapper(BlogMapper.class); 
Blog blog = mapper. findBlog(...);

Blog blog = Blog.queryByPrimaryKey(1, Blog.BELONGS_TO_AUTHOR);