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Mybatis 一對多和多對一關(guān)聯(lián)查詢問題

更新時間：2017年04月23日 14:12:31 作者：濫好人

這篇文章主要介紹了Mybatis 一對多和多對一關(guān)聯(lián)查詢問題,需要的朋友可以參考下

首先數(shù)據(jù)庫量表之間字段關(guān)系（沒有主外鍵）

studentmajor表的id字段對應(yīng)student表里major字段

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;
  }
}

定義兩個接口

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(jù)專業(yè)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(jù)主鍵查數(shù)據(jù),給多對一用
   * @param id
   * @return
   */
  public StudentMajor select(Integer id);
}

定義兩個實體類的映射方法

<?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">
  <!-- 多對一查詢 -->
  <resultMap type="Student" id="slist">
    <!-- 跟一對一一樣用association標簽,實體類定義的成員,要跟數(shù)據(jù)庫字段名對應(yīng)上 -->
    <association property="studentmajor" column="major" 
    select="com.dao.StudentMajorMapper.select"/> <!-- 用接口里定義的方法，根據(jù)student表中的major字段查出對應(yīng)數(shù)據(jù) -->
  </resultMap>
  <!-- 查全部 -->
  <select id="selectall" resultMap="slist" >
    select * from student
  </select>
  <!-- 根據(jù)專業(yè)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(guān)聯(lián) -->
   <resultMap type="StudentMajor" id="slist">
     <!-- 實體類屬性對應(yīng)數(shù)據(jù)庫的主鍵字段，不然主鍵會查不到 -->
     <id property="id" column="id"/>
     <!-- 用collection標簽 ,也是實體類屬性要對應(yīng)數(shù)據(jù)庫字段-->
     <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(jù)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(jù)專業(yè)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(jù)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(jié)果