sql插入表student的語句：

insert into student (id, name, tid) values ('9', '梁梁','2'); insert into student (id, name,tid) values ('7', '亮亮','2');

兩張表：




所對應的實體類，學術類：

package com.kuang.pojo;import lombok.Data;public class Student {private int id;private String name;@Overridepublic String toString() {return "Student{" +"id=" + id +", name='" + name + '\'' +", teacher=" + teacher +'}';}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Teacher getTeacher() {return teacher;}public void setTeacher(Teacher teacher) {this.teacher = teacher;}public Student(int id, String name, Teacher teacher) {this.id = id;this.name = name;this.teacher = teacher;};public Student(){};private Teacher teacher;//利用這個來做到一個老師關聯多個學生 }

老師:

package com.kuang.pojo;import lombok.Data;import java.util.List;@Data public class Teacher {private int id;private String name; private List<Student>stus;//一個老師關聯多個學生 }

多對一查詢語句：
sql編輯器下面輸入：

select s.id,s.name,t.name from student s,teacher t where s.tid = t.id;

顯示:

嵌套查詢：

按照查詢嵌套處理

目錄：

查詢所有的學生信息
根據查詢出來的學生tid,尋找對應的老師，子查詢：

<mapper namespace="com.kuang.dao.Studenmapper"> <select id="getstudent" resultMap="StudenTeacher">select * from student </select><resultMap id="StudenTeacher" type="com.kuang.pojo.Student"><result property="id" column="id"/><result property="name" column="name"/><association property="teacher" column="tid" javaType="com.kuang.pojo.Teacher" select="getTeacher"/></resultMap> <select id="getTeacher" resultType="com.kuang.pojo.Teacher">select * from teacher where id=#{id} </select> </mapper>

復雜的屬性，我們需要單獨處理，對象：association,集合:collection
測試類：

@Testpublic void testStudent(){SqlSession sqlSession = MybatisUtils.getSqlSession();Studenmapper stuma = sqlSession.getMapper(Studenmapper.class);List<Student> stu = stuma.getstudent();for(Student stu1:stu){System.out.println(stu1);}sqlSession.close();}

注意，type要用全類名，不然會報錯

按照結果嵌套處理

測試類：

@Testpublic void testStudent(){SqlSession sqlSession = MybatisUtils.getSqlSession();Studenmapper stuma = sqlSession.getMapper(Studenmapper.class);List<Student> stu = stuma.getstudent2();for(Student stu1:stu){System.out.println(stu1);}sqlSession.close();}

Studenmapper:

package com.kuang.dao; import com.kuang.pojo.Student;import java.util.List;public interface Studenmapper {public List<Student>getstudent();public List<Student>getstudent2(); }

xml:

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.kuang.dao.Studenmapper"> <select id="getstudent2" resultMap="StudenTeacher2">select s.id sid,s.name sname,t.name tnamefrom student s,teacher twhere s.tid=t.id; </select><resultMap id="StudenTeacher2" type="com.kuang.pojo.Student"><result property="id" column="sid"/><result property="name" column="sname"/><association property="teacher" javaType="com.kuang.pojo.Teacher" ><result property="name" column="tname"></result></association></resultMap></mapper>

這里因為把teacher拼成了teahcer導致報錯，還有注意type的寫法是全類名。
select s.id sid,s.name sname,t.name tname：
取了三個別名

總結

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