Mybatis - collection 一对多级联（单层级联、
2020-04-08 本文已影响0人
zbsong
上一节中说到了
association一对一级联，本节继续上一节的内容来实现collection一对多级联，本节继续使用上一节的demo
- 单层级联
-
新建一个主题表specials，与上一节中讲到的authors表形成一个一对多的关系，一个作者可以创建多个主题
image.png
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- 将specials表通过mybatis-generator生成对应的信息到项目中
- Special类内容如下
@Data
public class Special {
private String id;
private String name;
private String authorId;
}
- SpecialMapper 类内容如下
@Mapper
public interface SpecialMapper {
List<Special> getSpecialsByAuthorId(String authorId);
}
- SpecialMapper.xml 内容如下
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.sy.mybatis.mapper.SpecialMapper" >
<resultMap id="BaseResultMap" type="com.sy.mybatis.pojo.Special" >
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="author_id" property="authorId" jdbcType="VARCHAR" />
</resultMap>
<sql id="Base_Column_List" >
id, name, author_id
</sql>
<select id="getSpecialsByAuthorId" resultMap="BaseResultMap" parameterType="java.lang.String" >
select 'false' as QUERYID,
<include refid="Base_Column_List" />
from specials
where author_id = #{author_id,jdbcType=VARCHAR}
</select>
</mapper>
- 上面的内容就是平时普通用的，下面开始加入一对多级联的逻辑
- 编辑 Author类，添加specials属性，形成级联
@Data
public class Author {
private String id;
private String name;
private String loginName;
private String pwssword;
private AuthorInformation authorInformation;
private List<Special> specials;
}
- 编辑AuthorMapper.xml，在 <resultMap> 中加入<collection>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.sy.mybatis.mapper.AuthorMapper" >
<resultMap id="BaseResultMap" type="com.sy.mybatis.pojo.Author" >
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="login_name" property="loginName" jdbcType="VARCHAR" />
<result column="pwssword" property="pwssword" jdbcType="VARCHAR" />
<association property="authorInformation" column="id" select="com.sy.mybatis.mapper.AuthorInformationMapper.getAuthorInformationbyAuthorId"></association>
<collection property="specials" column="id" select="com.sy.mybatis.mapper.SpecialMapper.getSpecialsByAuthorId"></collection>
</resultMap>
<sql id="Base_Column_List" >
id, name, login_name, pwssword
</sql>
<select id="getAuthorById" resultMap="BaseResultMap" parameterType="java.lang.String" >
select 'false' as QUERYID,
<include refid="Base_Column_List" />
from authors
where id = #{id,jdbcType=VARCHAR}
</select>
</mapper>
<collection property="specials" column="id" select="com.sy.mybatis.mapper.SpecialMapper.getSpecialsByAuthorId"></collection>
select元素来指定指定的sql去查询
column传递给select语句的参数，多个参数，使用逗号分隔
与上一节中讲到的<association>一样的用法
测试
调用AuthorService的getAuthorById方法获取作者信息
image.png
可以看到在获取authors表信息的时候把specials对应的信息也查询了出来。
image.png
- 多层级联
-
新建一个文章表articles，与上面讲到的specials表形成一个多对多的关系，一个作者可以创建多个主题，一个主题可以有多篇文章
image.png
image.png
-
将articles表通过mybatis-generator生成对应的信息到项目中
-
Article类内容如下
@Data
public class Article {
private String id;
private String title;
private String specialId;
private String content;
}
- ArticleMapper 类内容如下
@Mapper
public interface ArticleMapper {
List<Article> getArticlesBySpecialId(String authorId);
}
- ArticleMapper.xml 内容如下
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.sy.mybatis.mapper.ArticleMapper" >
<resultMap id="BaseResultMap" type="com.sy.mybatis.pojo.Article" >
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="title" property="title" jdbcType="VARCHAR" />
<result column="special_id" property="specialId" jdbcType="VARCHAR" />
</resultMap>
<resultMap id="ResultMapWithBLOBs" type="com.sy.mybatis.pojo.Article" extends="BaseResultMap" >
<result column="content" property="content" jdbcType="LONGVARCHAR" />
</resultMap>
<sql id="Base_Column_List" >
id, title, special_id
</sql>
<sql id="Blob_Column_List" >
content
</sql>
<select id="getArticlesBySpecialId" resultMap="ResultMapWithBLOBs" parameterType="java.lang.String" >
select 'false' as QUERYID,
<include refid="Base_Column_List" />
,
<include refid="Blob_Column_List" />
from articles
where special_id = #{special_id,jdbcType=VARCHAR}
</select>
</mapper>
- 上面的内容就是平时普通用的，下面开始加入多对多级联的逻辑
- 编辑 Special类，添加articles属性，形成级联
@Data
public class Special {
private String id;
private String name;
private String authorId;
private List<Article> articles;
}
- 编辑SpecialMapper.xml，在 <resultMap> 中加入<collection>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.sy.mybatis.mapper.SpecialMapper" >
<resultMap id="BaseResultMap" type="com.sy.mybatis.pojo.Special" >
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="author_id" property="authorId" jdbcType="VARCHAR" />
<collection property="articles" column="id" select="com.sy.mybatis.mapper.ArticleMapper.getArticlesBySpecialId"></collection>
</resultMap>
<sql id="Base_Column_List" >
id, name, author_id
</sql>
<select id="getSpecialsByAuthorId" resultMap="BaseResultMap" parameterType="java.lang.String" >
select 'false' as QUERYID,
<include refid="Base_Column_List" />
from specials
where author_id = #{author_id,jdbcType=VARCHAR}
</select>
</mapper>
<collection property="articles" column="id" select="com.sy.mybatis.mapper.ArticleMapper.getArticlesBySpecialId"></collection>
select元素来指定指定的sql去查询
column传递给select语句的参数，多个参数，使用逗号分隔
测试
调用AuthorService的getAuthorById方法获取作者信息
image.png
可以看到在获取authors表信息的时候把special对应的信息也查询了出来,同时special与article的级联信息也一并查询出来了。
image.png
