Mybatis-技术专区-如何清晰的解决出现「多对一模型」和「一对多模型」的问题

基础使用篇

一对一

association

association通常用来映射一对一的关系，例如，有个类user,对应的实体类如下：

@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class Student {
    private int id;
    private String name;
    /**
     * 学生要关联一个老师
     */
    private Teacher teacher;
}
@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class Teacher {
    private int id;
    private String name;
}

Dao层进行Mapper查询操作

public interface TeacherMapper {
    Teacher getTeacher(@Param("tid") int id);
    Teacher getTeacher2(@Param("tid") int id);
}

Dao层进行Mapper.xml文件

 <resultMap id="StudentTeacher" type="com.sunreal.pojo.Student">
        <result column="id" property="id"></result>
        <result column="name" property="name"></result>
        <association property="teacher" column="id"  javaType="com.sunreal.pojo.Teacher" select="getTeacher"/>
    </resultMap>
    <select id="getStudent" resultMap="StudentTeacher">
        select *
        from student
    </select>
    <select id="getTeacher" resultType="com.sunreal.pojo.Teacher">
        select *
        from teacher
        where id = #{id}
    </select>
    <resultMap id="StudentTeacher2" type="com.sunreal.pojo.Student">
        <result column="sid" property="id"></result>
        <result column="sname" property="name"></result>
        <association property="teacher" javaType="com.sunreal.pojo.Teacher">
            <result property="name" column="tname"></result>
        </association>
    </resultMap>
    <select id="getStudent2" resultMap="StudentTeacher2">
        select s.id sid, s.name sname, t.name tname
        from student s,
             teacher t
        where s.tid = t.id
    </select>

assocication：可以指定联合的JavaBean对象

select：指定相关查询结果sqlid
property="role“：指定哪个属性是联合的对象
javaType:指定这个属性对象的类型
column="{javabean熟悉=数据库字段,Javabean属性=数据库字段}"

<association property="role" javaType="com.queen.mybatis.bean.Role">
    <id column="role_id" property="id"/>
    <result column="roleName" property="roleName"/>
</association>

以上如果跨越命名空间的情况下：select：需要用namespace.selectId进行指定。

https://www.cnblogs.com/liboware/p/15220433.html

故乡明