Mybatis - association 一对一级联
2020-04-08 本文已影响0人
zbsong
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实际操作中，我能需要先确定对象的关系，先创建两张表，模拟一个一对一的对象关系。
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（随便定义的，只为了演示）
authors：作者表，存储姓名、登录名、密码
authorInformations：作者信息表，存储年龄、座右铭
上面两张表是一对一的关系，一个作者只对应一条信息记录
- 新建一个Spring Boot工程，命名为mybatis_cascade（随意）
- 配置项目，并且通过mybatis-generator生成上面说的两个类的信息，步骤略...
- Author类内容如下
@Data
public class Author {
private String id;
private String name;
private String loginName;
private String pwssword;
//添加authorInformation属性，形成级联
private AuthorInformation authorInformation;
}
- AuthorInformation类内容如下
@Data
public class AuthorInformation {
private String id;
private String authorId;
private Integer age;
private String motto;
}
- AuthorMapper内容如下（为了方便查看，将默认生成的方法都删掉了，下面几个文件的内容也是一样都删掉了，新建了一个方法，根据ID 查询作者的信息）
@Mapper
public interface AuthorMapper {
Author getAuthorById(String id);
}
- AuthorInformationMapper类内容如下
@Mapper
public interface AuthorInformationMapper {
AuthorInformation getAuthorInformationbyAuthorId(String authorId);
}
- AuthorMapper.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.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>
</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>
9.AuthorInformationMapper.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.AuthorInformationMapper" >
<resultMap id="BaseResultMap" type="com.sy.mybatis.pojo.AuthorInformation" >
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="author_id" property="authorId" jdbcType="VARCHAR" />
<result column="age" property="age" jdbcType="INTEGER" />
<result column="motto" property="motto" jdbcType="VARCHAR" />
</resultMap>
<sql id="Base_Column_List" >
id, author_id, age, motto
</sql>
<select id="getAuthorInformationbyAuthorId" resultMap="BaseResultMap" parameterType="java.lang.String" >
select 'false' as QUERYID,
<include refid="Base_Column_List" />
from author_informations
where author_id = #{authorId,jdbcType=VARCHAR}
</select>
</mapper>
.xml文件创建完以后，来看一下AuthorMapper.xml文件中resultMap的<association/>。
<association property="authorInformation" column="id" select="com.sy.mybatis.mapper.AuthorInformationMapper.getAuthorInformationbyAuthorId"></association>
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
- 创建Service来获取作者信息
@Service
public class AuthorService {
@Autowired
private AuthorMapper authorMapper;
public Author getAuthorById(String id) {
Author author = authorMapper.getAuthorById(id);
return author;
}
}
测试
调用AuthorService的getAuthorById方法获取作者信息
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可以看到在获取authors表信息的时候把authorInformations对应的信息也查询了出来。
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