Mybatis 一對一、一對多、多對一
阿新 • • 發佈：2018-12-25
靈感來源於：https://www.cnblogs.com/xdp-gacl/p/4264440.html
轉發自：https://www.cnblogs.com/hq233/p/6752335.html
首先 資料庫量表之間欄位關係（沒有主外來鍵）
studentmajor表的id欄位對應student表裡major欄位
兩個實體類
package com.model;
import java.util.Date;
public class Student {
private Integer sno;
private String sname;
private String ssex;
private Integer sclass;
private StudentMajor studentmajor;
public Student() {
super();
}
public Student(Integer sno, String sname, String ssex, Integer sclass, StudentMajor studentmajor) {
super();
this.sno = sno;
this.sname = sname;
this.ssex = ssex;
this.sclass = sclass;
this.studentmajor = studentmajor;
}
public StudentMajor getStudentmajor() {
return studentmajor;
}
public void setStudentmajor(StudentMajor studentmajor) {
this.studentmajor = studentmajor;
}
public Integer getSno() {
return sno;
}
public void setSno(Integer sno) {
this.sno = sno;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public String getSsex() {
return ssex;
}
public void setSsex(String ssex) {
this.ssex = ssex;
}
@Override
public String toString() {
return "Student [sno=" + sno + ", sname=" + sname + ", ssex=" + ssex + ", sclass=" + sclass + ", studentmajor="
+ studentmajor + "]";
}
public Integer getSclass() {
return sclass;
}
public void setSclass(Integer sclass) {
this.sclass = sclass;
}
}
package com.model;
import java.util.List;
public class StudentMajor {
private Integer id;
private String mcode;
private String mname;
private List<Student> students;
public StudentMajor() {
super();
}
public StudentMajor(Integer id, String mcode, String mname, List<Student> students) {
super();
this.id = id;
this.mcode = mcode;
this.mname = mname;
this.students = students;
}
@Override
public String toString() {
return "StudentMajor [id=" + id + ", mcode=" + mcode + ", mname=" + mname + ", students=" + students + "]";
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getMcode() {
return mcode;
}
public void setMcode(String mcode) {
this.mcode = mcode;
}
public String getMname() {
return mname;
}
public void setMname(String mname) {
this.mname = mname;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
}
定義兩個介面
package com.dao;
import java.util.List;
import java.util.Map;
import com.model.Student;
public interface StudentMapper {
/**
* 全表查詢
*/
public List<Student> selectall();
/**
* 根據專業查人員,給一對多用
*/
public List<Student> selectz(Integer major);
}
package com.dao;
import java.util.List;
import com.model.StudentMajor;
public interface StudentMajorMapper {
/**
* 全表查詢
* @return
*/
public List<StudentMajor> selectAll();
/**
* 根據主鍵查資料,給多對一用
* @param id
* @return
*/
public StudentMajor select(Integer id);
}
定義兩個實體類的對映方法
<?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.dao.StudentMapper">
<!-- 多對一查詢 -->
<resultMap type="Student" id="slist">
<!-- 跟一對一一樣用association標籤,實體類定義的成員,要跟資料庫欄位名對應上 -->
<association property="studentmajor" column="major"
select="com.dao.StudentMajorMapper.select"/> <!-- 用接口裡定義的方法，根據student表中的major欄位查出對應資料 -->
</resultMap>
<!-- 查全部 -->
<select id="selectall" resultMap="slist" >
select * from student
</select>
<!-- 根據專業查人員 -->
<select id="selectz" parameterType="Integer" resultType="student">
select * from student s where s.major=#{major}
</select>
</mapper>
<?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.dao.StudentMajorMapper">
<!-- 一對多查詢關聯 -->
<resultMap type="StudentMajor" id="slist">
<!-- 實體類屬性對應資料庫的主鍵欄位，不然主鍵會查不到 -->
<id property="id" column="id"/>
<!-- 用collection標籤 ,也是實體類屬性要對應資料庫欄位-->
<collection property="students" column="id"
select="com.dao.StudentMapper.selectz">
</collection>
</resultMap>
<!-- 全表查詢 -->
<select id="selectAll" resultMap="slist">
select * from studentmajor
</select>
<!-- 根據主鍵查 -->
<select id="select" parameterType="Integer" resultType="StudentMajor">
select * from studentmajor where id=#{id}
</select>
</mapper>
JUnit測試
package com.util;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.dao.StudentMajorMapper;
import com.dao.StudentMapper;
import com.model.Student;
import com.model.StudentMajor;
public class JJJtest {
private SqlSession ss;
private StudentMapper sm;
private StudentMajorMapper smm;
@Before
public void setUp() throws Exception {
ss=SqlSessionUtil.getSqlSession();
sm=ss.getMapper(StudentMapper.class);
smm=ss.getMapper(StudentMajorMapper.class);
}
@After
public void tearDown() throws Exception {
ss.commit();
ss.close();
}
//一對多查詢
public void test() {
List<StudentMajor> list=smm.selectAll();
for(StudentMajor a:list){
System.out.println(a);
}
}
//根據專業查人員，給一對多用
public void selectz(){
List<Student> l=sm.selectz(3);
for(Student a:l){
System.out.println(a);
}
}
//多對一查詢
@Test
public void selectall() {
List<Student> st=sm.selectall();
for(Student tt:st){
System.out.println(tt);
}
}
//根據主鍵查詢，給多對一用
public void select(){
StudentMajor a=smm.select(1);
System.out.println(a);
}
}
一對多查詢結果
多對一查詢結果
