Mybatis---复杂sql应用

1、多对一处理

• 编写实体类

  package com.ss.pojo;
  
  import lombok.AllArgsConstructor;
  import lombok.Data;
  import lombok.NoArgsConstructor;
  
  @Data 
  @NoArgsConstructor
  @AllArgsConstructor
  public class Student {
      
      private int id;
      private String name;
      private Teacher teacher;
  }
  

  package com.ss.pojo;
  
  import lombok.AllArgsConstructor;
  import lombok.Data;
  import lombok.NoArgsConstructor;
  
  @Data
  @NoArgsConstructor
  @AllArgsConstructor
  public class Teacher {
      
      private int id;
      private String name;
      
  }
  

• 编写工具类 MybaitsUtils

• 编写配置文件

• 编写实体类对应的Mapper接口 和 Mapper.xml文件

<?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.ss.dao.StudentMapper">

    <!--
        1.查询出所有学生的信息
        2.根据tid，查询对应的老师
    -->
    <select id="getAllStudent" resultMap="StudentTeacher">
        select * from student
    </select>

    <resultMap id="StudentTeacher" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--复杂的属性   子查询
                对象：association
                集合：collection
        -->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>

    <select id="getTeacher" resultType="Teacher">
        select * from teacher where id = #{id}
    </select>
<!--====================================================================================================-->
    <!--嵌套查询-->
    <select id="getAllStudent2" resultMap="StudentTeacher2">
        select s.id sid,s.name sname,t.name tname,t.id tid 
        from student s,teacher t 
        where s.tid = t.id
    </select>
    <resultMap id="StudentTeacher2" type="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="id" column="tid"/>
            <result property="name" column="tname"/>
        </association>
    </resultMap>
</mapper>

• 编写测试类

2、一对多处理

• 编写实体类

  package com.ss.pojo;
  
  import lombok.AllArgsConstructor;
  import lombok.Data;
  import lombok.NoArgsConstructor;
  
  import java.util.List;
  
  @Data
  @NoArgsConstructor
  @AllArgsConstructor
  public class Teacher {
      
      private int id;
      private String name;
      private List<Student> students;
      
  }
  

  package com.ss.pojo;
  
  import lombok.AllArgsConstructor;
  import lombok.Data;
  import lombok.NoArgsConstructor;
  
  @Data
  @NoArgsConstructor
  @AllArgsConstructor
  public class Student {
      
      private int id;
      private String name;
      private int tid; 
  }
  

• 编写工具类 MybaitsUtils

• 编写配置文件

• 编写实体类对应的Mapper接口 和 Mapper.xml文件

  <?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.ss.dao.TeacherMapper">
      
  <!--嵌套查询-->
      <select id="getTeacher" resultMap="TeacherStudent">
          select s.id sid,s.name sname ,t.name tname ,t.id tid
          from teacher t,student s
          where s.tid = t.id and t.id = #{tid}
      </select>
      <resultMap id="TeacherStudent" type="Teacher">
          <result property="id" column="tid"/>
          <result property="name" column="tname"/>
          <collection property="students" ofType="Student">
              <result property="id" column="sid"/>
              <result property="name" column="sname"/>
              <result property="tid" column="tid"/>
          </collection>
      </resultMap>
  <!--====================================================================================================-->
      <!--子查询-->
      <select id="getTeacher2" resultMap="TS">
          select * from teacher where id = #{tid}
      </select>
      <resultMap id="TS" type="Teacher">
          <result property="id" column="id"/>
          <result property="name" column="name"/>
          <collection property="students" ofType="Student" javaType="ArrayList" select="getStudentByid" column="id"/>
      </resultMap>
      <select id="getStudentByid" resultType="Student">
          select * from student where tid = #{tid}
      </select>
  </mapper>
  

• 编写测试类