Mybatis 高级结果映射 ResultMap Association Collection - ilovejava.docxVIP

Mybatis 高级结果映射 ResultMap Association Collection - ilovejavaMyBatis的创建基于这样一个思想：数据库并不是您想怎样就怎样的。虽然我们希望所有的数据库遵守第三范式或BCNF（修正的第三范式），但它们不是。如果有一个数据库能够完美映射到所有应用程序，也将是非常棒的，但也没有。结果集映射就是MyBatis为解决这些问题而提供的解决方案。例如，我们如何映射下面这条语句？[java]!-- Very Complex Statement -- select id=selectBlogDetails parameterType=int resultMap=detailedBlogResultMap select B.id as blog_id, B.title as blog_title, B.author_id as blog_author_id, A.id as author_id, A.username as author_username, A.password as author_password, A.email as author_email, A.bio as author_bio, A.favourite_section as author_favourite_section, P.id as post_id, P.blog_id as post_blog_id, P.author_id as post_author_id, P.created_on as post_created_on, P.section as post_section, P.subject as post_subject, P.draft as draft, P.body as post_body, C.id as comment_id, C.post_id as comment_post_id, C.name as comment_name, C.comment as comment_text, T.id as tag_id, T.name as tag_name from Blog B left outer join Author A on B.author_id = A.id left outer join Post P on B.id = P.blog_id left outer join Comment C on P.id = C.post_id left outer join Post_Tag PT on PT.post_id = P.id left outer join Tag T on PT.tag_id = T.id where B.id = #{id} /select您可能想要把它映射到一个智能的对象模型，包括由一个作者写的一个博客，有许多文章（Post，帖子），每个文章由0个或者多个评论和标签。下面是一个复杂ResultMap 的完整例子（假定作者、博客、文章、评论和标签都是别名）。仔细看看这个例子，但是不用太担心，我们会一步步地来分析，一眼看上去可能让人沮丧，但是实际上非常简单的[java]!-- Very Complex Result Map -- resultMap id=detailedBlogResultMap type=Blog constructor idArg column=blog_id javaType=int/ /constructor result property=title column=blog_title/ association property=author column=blog_author_id javaType= Author id property=id column=author_id/ result property=username column=author_username/ result property=password column=author_password/ result property=email column=author_email/ result property=bio column=author_bio/ result property=favouriteSection column=author_favourite_section/ /association collection property=posts ofType=Post id property=id column=post_id/ result property=subject column=post_subject/