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
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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; }} |
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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; }} |
定义两个接口
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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);} |
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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);} |
定义两个实体类的映射方法
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<?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> |
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<?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> |
JUnit测试
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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); }} |
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服务器之家网站的支持！
原文链接：http://www.cnblogs.com/hq233/archive/2017/04/23/6752335.html
