Mybatis关联、集合查询

关联查询（一对一）

场景：一个作者(Author)有一个博客(Blog)

Blog.java

    public class Blog {        private String id;        private String authorId;        private Author author;        //get & set    }

BlogMapper.xml

<resultMap id="blogResult" type="Blog">  <association property="author" column="author_id" javaType="Author" select="authorMapper.selectAuthor"/></resultMap><select id="selectBlog" resultMap="blogResult">  SELECT * FROM BLOG WHERE ID = #{id}</select>

AuthorMapper.xml

<mapper namespace="authorMapper" >    <select id="selectAuthor" resultType="Author">      SELECT * FROM AUTHOR WHERE ID = #{id}    </select></mapper>

调用BlogMapper.xml中selectBlog 就可以查询关联后的结果。

集合查询（一对多）

场景：一个博客(Blog)有多篇文章(Post)

Blog.java

    public class Blog {        private String id;        private List<Post> posts;        //get & set    }

BlogMapper.xml

<resultMap id="blogResult" type="Blog">  <collection property="posts" javaType="ArrayList" column="id" ofType="Post" select="postMapper.selectPostsForBlog"/></resultMap><select id="selectBlog" resultMap="blogResult">  SELECT * FROM BLOG WHERE ID = #{id}</select>

PostMapper.xml

<mapper namespace="postMapper" >    <select id="selectPostsForBlog" resultType="Post">      SELECT * FROM POST WHERE BLOG_ID = #{id}    </select></mapper>

调用BlogMapper.xml中selectBlog就可以查询集合后的结果。

注意：column属性值为数据库中表所对应的列名。