03第三章MyBatis高级映射association&collection[一对一、一对多（嵌套查询)]_<collection>标签中可以嵌套 <association>吗-优快云博客

本文链接：https://blog.youkuaiyun.com/BiuBiuyu/article/details/115518073

文章目录

一、一对一映射

//实体列 class Tb_blog/TbBlog
    private long blogId;
    private String blogTitle;
    private String blogContent;
    private Date createTime;
    private  String blogType;
    private String sId;

    private Tb_author author;
    List<TbAuthor> tbAuthorList;
    //要写get、set方法 此处省略....

//实体类 class TbAuthor  
    private long id;
    private String username;
    private String password;
    private String email;
    private String address;
    private String phone;
    
    private TbBlog tbBlog;
    private List<TbBlog> tbBlogList;
//要写get、set方法 此处省略....

1.resultMap标签配置

 <!-- xml -->
 <resultMap id="blogMap" type="Tb_blog"  >
            <id column="blogId" property="blogId"/>
            <result column="blogTitle" property="blogTitle"/>
            <result column="blogContent"  property="blogContent"/>
            <result column="blogType"  property="blogType"/>
            <result column="createTime"  property="createTime"/>
     	    <result column="sId"	property="sId"/>
            <result column="id"	property="author.id"/> <!-- 映射第二张表的实体类属性 -->
     	   	<result column="username"	property="author.username"/>
     	    <result column="password"	property="author.password"/>
    	    <result column="email"	property="author.email"/>
     
</resultMap>
    <select id="selectBlogAndAuthor" resultMap="blogMap">
        select * from tb_blog g inner join tb_author r
        on g.blogId = r.id 
    </select>

2.association标签配置

 <!-- xml --> 
<resultMap id="blogMap" type="Tb_blog"  >
            <id column="blogId" property="blogId"/>
            <result column="blogTitle" property="blogTitle"/>
            <result column="blogContent"  property="blogContent"/>
            <result column="blogType"  property="blogType"/>
            <result column="createTime"  property="createTime"/>
            <!--        一对一高效率写法 association一对一关联  property属性为实体类中的第二张表的属性名   -->
            <association   property="tb_author" javaType="Tb_author"><!--javaType属性为 返回的实体类对象 -->
                <id column="id"  property="id"/>
                <result column="username" property="username"/>
                <result column="password" property="password"/>
                <result column="email" property="email"/>
                <result column="address" property="address"/>

            </association>
</resultMap>
    <select id="selectBlogAndAuthor" resultMap="blogMap">
        select * from tb_blog g inner join tb_author r on g.blogId = r.id 
    </select>

3.association多表一对一嵌套查询

//AuthorMapper.interface
	//!通过id 和映射文件中 association的column属性的值sId关联 来嵌套查询     嵌套查询的第二条sql语句都要写条件来关联第一张表
    List<TbAuthor> selectAuthorandBlogAssociation(int id);

//BlogMapper.interface
	List<TbBlog> selectBlogAndAuthorAssociation();

<!-- AuthorMapper.xml -->
    <select id="selectAuthorandBlogAssociation" resultType="com.xqh.pojo.TbAuthor">
        select * from tb_author where id=#{id}
    </select>

<!-- BlogMapper.xml -->
  <resultMap id="mapAssociation" type="TbBlog">
        <id property="blogId" column="blogId"/>
        <id property="blogTitle" column="blogTitle"/>
        <id property="blogContent" column="blogContent"/>
        <id property="createTime" column="createTime"/>
        <id property="blogType" column="blogType"/>
        <id property="sId" column="sId"/>
		
      	//一对一 association.property属性 用的是单个对象 
        <association property="tbAuthor" column="sId" javaType="TbAuthor"
                     select="com.xqh.mapper.AuthorMapper.selectAuthorandBlogAssociation">
            <id property="id" column="id"/>
            <result property="username" column="username"/>
            <result property="password" column="password"/>
            <result property="phone" column="phone"/>
            <result property="email" column="email"/>
            <result property="address" column="address"/>

        </association>
    </resultMap>
    <select id="selectBlogAndAuthorAssociation" resultMap="mapAssociation">
        select * from tb_blog
    </select>

二、一对多查询

//实体列
  private long id;
  private String username;
  private String password;
  private String email;
  private String address;
  private String phone;
  private TbBlog tbBlog;

  private List<TbBlog> tbBlogList;

1.collection标签多表连接查询(一对多)

//AuthorMapper.interface
//    一对多sql笛卡尔积多表查询
    List<TbAuthor> selectAuthor_BlogList2();

<!-- xml -->
<!--    一对多sql笛卡尔积多表查询-->
    <resultMap id="mapCollection2" type="TbAuthor">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="password" column="password"/>
        <result property="email" column="email"/>
        <result property="phone" column="phone"/>
        <result property="address" column="address"/>
        
        //一对多 collection.property用的是集合对象 来返回多条数据
        <collection property="tbBlogList" column="id" ofType="TbBlog">
            <id property="blogId" column="blogId"/>
            <result property="blogTitle" column="blogTitle"/>
            <result property="blogContent" column="blogContent"/>
            <result property="blogType" column="blogType"/>
            <result property="createTime" column="vreateTime"/>
            <result property="sId"  column="sId"/>
        </collection>
    </resultMap>

    <select id="selectAuthor_BlogList2" resultMap="mapCollection2">
        select * from tb_author inner join tb_blog tb on tb_author.id = tb.sId
    </select>

2.collection多表嵌套查询(一对多)

//AuthorMapper.interface
    List<TbAuthor> selectAuthor_BlogList();

//BlogMapper.interface
//    一对多嵌套查询 id是给限制 不然一个作者全部博客
    List<TbBlog> selectBlogAndAuthor(int id);

<!-- BlogMapper.xml-->
    <select id="selectBlogAndAuthor" resultType="com.xqh.pojo.TbBlog">
        select * from tb_blog where sId = #{id}
    </select>

<!-- xml -->
<!--    AuthorMapper.xml-->
    <resultMap id="mapCollection" type="TbAuthor">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="password" column="password"/>
        <result property="email" column="email"/>
        <result property="phone" column="phone"/>
        <result property="address" column="address"/>
        <collection property="tbBlogList" column="id"
            select="com.xqh.mapper.BlogMapper.selectBlogAndAuthor"
                    fetchType="lazy">

        </collection>
    </resultMap>

    <select id="selectAuthor_BlogList" resultMap="mapCollection">
        select * from tb_author
    </select>

三、总结

1.多表查询一对一映射

association标签

不嵌套 property=当前实体类中的第二种表的属性名 javaType=返回的实体类
嵌套多加两个属性 column=当前实体类关联的第二张表的外键字段 select=“第二条查询语句” (必须给第二条sql语句写参数限制不然会获得所有值)

2.多表查询一对多

collection标签

不嵌套 property=当前实体类中的第二种表的属性名 ofType=返回是实体类
property=当前实体类中的第二种表的属性名 javaType=返回的实体类
嵌套多加两个属性 column=当前实体类关联的第二张表的外键字段 select=“第二条查询语句” (必须给第二条sql语句写参数限制不然会获得所有值)

2.多表查询一对多

collection标签

不嵌套 property=当前实体类中的第二种表的属性名 ofType=返回是实体类
嵌套多加一个属性 column=当前实体类关联的第二张表的外键字段 select=“第二条查询语句” (必须给第二条sql语句写参数限制不然会获得所有值) [ofType = collection一对多嵌套查询嵌套查询所有结果不需写返回类型因为 select已经映射]