Mybatis實現(xiàn)關(guān)聯(lián)關(guān)系映射的方法示例

更新時間：2022年07月18日 14:21:49 作者：aigo-2021

本文主要介紹了Mybatis實現(xiàn)關(guān)聯(lián)關(guān)系映射的方法示例，文中通過示例代碼介紹的非常詳細(xì)，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

數(shù)據(jù)庫表結(jié)構(gòu)

tb_project

tb_cmpany

一、實現(xiàn)Project關(guān)聯(lián)Company一對一關(guān)聯(lián)

Company.java

package com.hyxy.po;
 
import java.util.List;
 
public class Company {
    private int cId;
    private String cName;
 
    public int getcId() {
        return cId;
    }
 
    public void setcId(int cId) {
        this.cId = cId;
    }
 
    public String getcName() {
        return cName;
    }
 
    public void setcName(String cName) {
        this.cName = cName;
    }
}

Project.java

Project中聲明Company類型的屬性

package com.hyxy.po;
 
public class Project {
    private int pId;
    private String projectName;
    private int cId;
    private int empId;
    private int amt;
    private Company company;
 
    public Company getCompany() {
        return company;
    }
 
    public void setCompany(Company company) {
        this.company = company;
    }
 
    public int getpId() {
        return pId;
    }
 
    public void setpId(int pId) {
        this.pId = pId;
    }
 
    public String getProjectName() {
        return projectName;
    }
 
    public void setProjectName(String projectName) {
        this.projectName = projectName;
    }
 
    public int getcId() {
        return cId;
    }
 
    public void setcId(int cId) {
        this.cId = cId;
    }
 
    public int getEmpId() {
        return empId;
    }
 
    public void setEmpId(int empId) {
        this.empId = empId;
    }
 
    public int getAmt() {
        return amt;
    }
 
    public void setAmt(int amt) {
        this.amt = amt;
    }
}

ProjectDao.java

package com.hyxy.dao;
 
import com.hyxy.po.Project;
 
import java.util.List;
 
public interface ProjectDao {
    public List<Project> select();
}

ProjectMapper.xml

<?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">
<!--所有映射文件中的sql語句，為了區(qū)分多個映射文件，使用命名空間+id進(jìn)行區(qū)分。namespace命名空間-->
<mapper namespace="com.hyxy.dao.CompanyDao">
    <!--自定義結(jié)果映射-->
    <resultMap id="resultMap" type="com.hyxy.po.Company">
        <!--如果數(shù)據(jù)庫中有主鍵，寫id映射-->
        <id column="companyid" property="cId"></id>
        <result column="companyname" property="cName"></result>
        <!--一對多關(guān)系映射  （全類名.resultMap）-->
        <collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
        </collection>
 
    </resultMap>
    <!--
        查詢所有的項目信息，多表連接查詢關(guān)聯(lián)的客戶信息，
        把項目信息注入到Project對象中，把客戶信息注入到Company對象中
        Company對象注入到Project對象的company屬性中
    -->
    <select id="select" resultMap="resultMap">
        select * from tb_company c
        inner join tb_project p on p.companyid=c.companyid
 
    </select>
 
</mapper>

Test1.java

package com.hyxy;
 
import com.hyxy.dao.ProjectDao;
 
import com.hyxy.po.Project;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import java.io.IOException;
import java.io.Reader;
import java.util.List;
//接口綁定，動態(tài)查詢，關(guān)聯(lián)關(guān)系查詢
public class Test1 {
    public static void main(String[] args) {
        Reader reader=null;
        try{
            reader= Resources.getResourceAsReader("configuration.xml");
            SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
            SqlSession sqlSession=sqlSessionFactory.openSession();
            //一對一
            ProjectDao projectDao=sqlSession.getMapper(ProjectDao.class);
            List<Project> list =projectDao.select();
            for(Project p:list){
                System.out.println(p.getcId()+","+p.getProjectName()+","+p.getCompany().getcName());
            }
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}

運行結(jié)果：

或者

ProjectMapper.xml

<!-- 使用已經(jīng)定義好的一個 resultMap -->
<association property="company" resultMap="com.hyxy.dao.CompanyDao.resultMap">
</association>

CompanyMapper.xml

<mapper namespace="com.hyxy.dao.CompanyDao">
    <resultMap id="resultMap" type="com.hyxy.po.Company">
        <id column="companyid" property="cId"></id>
        <result column="companyname" property="cname"></result>
    </resultMap>
</mapper>

二、實現(xiàn)Company關(guān)聯(lián)Project一對多關(guān)系

Company類中聲明 List<Project> 屬性

Company.java

package com.hyxy.po;
 
import java.util.List;
 
public class Company {
    private int cId;
    private String cName;
    private List<Project> list;//實現(xiàn)Company關(guān)聯(lián)Project 一對多
 
    public List<Project> getList() {
        return list;
    }
 
    public void setList(List<Project> list) {
        this.list = list;
    }
 
    public int getcId() {
        return cId;
    }
 
    public void setcId(int cId) {
        this.cId = cId;
    }
 
    public String getcName() {
        return cName;
    }
 
    public void setcName(String cName) {
        this.cName = cName;
    }
}

CompanyDao.java

package com.hyxy.dao;
 
import com.hyxy.po.Company;
 
import java.util.List;
 
public interface CompanyDao {
    public List<Company> select();
}

CompanyMapper.xml

<?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">
<!--所有映射文件中的sql語句，為了區(qū)分多個映射文件，使用命名空間+id進(jìn)行區(qū)分。namespace命名空間-->
<mapper namespace="com.hyxy.dao.CompanyDao">
    <!--自定義結(jié)果映射-->
    <resultMap id="resultMap" type="com.hyxy.po.Company">
        <!--如果數(shù)據(jù)庫中有主鍵，寫id映射-->
        <id column="companyid" property="cId"></id>
        <result column="companyname" property="cName"></result>
        <!--一對多關(guān)系映射  （全類名.resultMap）-->
        <collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
        </collection>
 
    </resultMap>
    <select id="select" resultMap="resultMap">
        select * from tb_company c
        inner join tb_project p on p.companyid=c.companyid
 
    </select>
 
</mapper>

Test2.java

package com.hyxy;
 
import com.hyxy.dao.CompanyDao;
import com.hyxy.po.Company;
import com.hyxy.po.Project;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 
import java.io.IOException;
import java.io.Reader;
import java.util.List;
 
//接口綁定，動態(tài)查詢，關(guān)聯(lián)關(guān)系查詢
public class Test2 {
    public static void main(String[] args) {
        Reader reader=null;
        try{
            reader= Resources.getResourceAsReader("configuration.xml");
            SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
            SqlSession sqlSession=sqlSessionFactory.openSession();
            //一對多
            CompanyDao companyDao=sqlSession.getMapper(CompanyDao.class);
            List<Company> list= companyDao.select();
            for(Company c:list){
                System.out.println(c.getcName());
                for(Project p:c.getList()){
                    System.out.println(p.getProjectName());
                }
                System.out.println("--------------------");
            }
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}

運行結(jié)果：

一對一關(guān)聯(lián)使用<association>，一對多關(guān)聯(lián)使用<collection>

三、Mybatis子查詢方式實現(xiàn)關(guān)聯(lián)關(guān)系查詢

ProjectMapper.xml

<association property="company" javaType="com.hyxy.po.Company" column="companyid" select="com.hyxy.dao.CompanyDao.selectById">
</association>

<select id="select" resultMap="resultMap">
    select * from tb_project
</select>

CompanyMapper.xml

<mapper namespace="com.hyxy.dao.CompanyDao">
    <resultMap id="resultMap" type="com.hyxy.po.Company">
        <id column="companyid" property="companyId"></id>
        <result column="companyname" property="companyName"></result>
        <collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap">
    </collection>
    </resultMap>
    <select id="select" resultMap="resultMap">
        select * from tb_company c inner join tb_project p on c.companyid = p.companyid
    </select>
    <select id="selectById" resultMap="resultMap" parameterType="int">
        select * from tb_company where companyid = #{id}
    </select>
</mapper>

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