滥好人 通过本文主要向大家介绍了mybatis面试问题,mybatis一对多关联,mybatis多表关联查询,mybatis关联查询,mybatis关联映射等相关知识,希望对您有所帮助,也希望大家支持linkedu.com www.linkedu.com
首先 数据库量表之间字段关系（没有主外键）
studentmajor表的id字段对应student表里major字段
两个实体类
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;
}
}
</div>
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;
}
}
</div>
定义两个接口
package com.dao;
import java.util.List;
import java.util.Map;
import com.model.Student;
public interface StudentMapper {
/**
* 全表查询
*/
public List<Student> selectall();
/**
* 根据专业查人员,给一对多用
*/
public List<Student> selectz(Integer major);
}
</div>
package com.dao;
import java.util.List;
import com.model.StudentMajor;
public interface StudentMajorMapper {
/**
* 全表查询
* @return
*/
public List<StudentMajor> selectAll();
/**
* 根据主键查数据,给多对一用
* @param id
* @return
*/
public StudentMajor select(Integer id);
}
</div>
定义两个实体类的映射方法
<?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">
<!-- 多对一查询 -->
<resultMap type="Student" id="slist">
<!-- 跟一对一一样用association标签,实体类定义的成员,要跟数据库字段名对应上 -->
<association property="studentmajor" column="major"
select="com.dao.StudentMajorMapper.select"/> <!-- 用接口里定义的方法，根据student表中的major字段查出对应数据 -->
</resultMap>
<!-- 查全部 -->
<select id="selectall" resultMap="slist" >
select * from student
</select>
<!-- 根据专业查人员 -->
<select id="selectz" parameterType="Integer" resultType="student">
select * from student s where s.major=#{major}
</select>
</mapper>
</div>
<?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">
<!-- 一对多查询关联 -->
<resultMap type="StudentMajor" id="slist">
<!-- 实体类属性对应数据库的主键字段，不然主键会查不到 -->
<id property="id" column="id"/>
<!-- 用collection标签 ,也是实体类属性要对应数据库字段-->
<collection property="students" column="id"
select="com.dao.StudentMapper.selectz">
</collection>
</resultMap>
<!-- 全表查询 -->
<select id="selectAll" resultMap="slist">
select * from studentmajor
</select>
<!-- 根据主键查 -->
<select id="select" parameterType="Integer" resultType="StudentMajor">
select * from studentmajor where id=#{id}
</select>
</mapper>
</div>
JUnit测试
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();
}
//一对多查询
public void test() {
List<StudentMajor> list=smm.selectAll();
for(StudentMajor a:list){
System.out.println(a);
}
}
//根据专业查人员，给一对多用
public void selectz(){
List<Student> l=sm.selectz(3);
for(Student a:l){
System.out.println(a);
}
}
//多对一查询
@Test
public void selectall() {
List<Student> st=sm.selectall();
for(Student tt:st){
System.out.println(tt);
}
}
//根据主键查询，给多对一用
public void select(){
StudentMajor a=smm.select(1);
System.out.println(a);
}
}
</div>
一对多查询结果
多对一查询结果
以上所述是小编给大家介绍的Mybatis 一对多和多对一关联查询问题，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对网站的支持！
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