Mybatis实现关联关系映射的方法示例
作者:aigo-2021
本文主要介绍了Mybatis实现关联关系映射的方法示例,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友们下面随着小编来一起学习学习吧
类和类有关联,将查询的结果注入到对象和对象的关联关系中
Mybatis处理的关联关系 包括一对一关联 和 一对多关联 ,例如学生关联班级是一对一 ;班级关联学生是一对多。
Mybatis实现关联关系映射,有两种方式:多表连接
和 子查询
数据库表结构
tb_project
tb_cmpany
一、实现Project关联Company一对一关联
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中声明Company类型的属性
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语句,为了区分多个映射文件,使用命名空间+id进行区分。namespace命名空间--> <mapper namespace="com.hyxy.dao.CompanyDao"> <!--自定义结果映射--> <resultMap id="resultMap" type="com.hyxy.po.Company"> <!--如果数据库中有主键,写id映射--> <id column="companyid" property="cId"></id> <result column="companyname" property="cName"></result> <!--一对多关系映射 (全类名.resultMap)--> <collection property="list" resultMap="com.hyxy.dao.ProjectDao.resultMap"> </collection> </resultMap> <!-- 查询所有的项目信息,多表连接查询关联的客户信息, 把项目信息注入到Project对象中,把客户信息注入到Company对象中 Company对象注入到Project对象的company属性中 --> <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; //接口绑定,动态查询,关联关系查询 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(); //一对一 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(); } } }
运行结果:
或者
ProjectMapper.xml
<!-- 使用已经定义好的一个 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、实现Company关联Project一对多关系
Company类中声明 List<Project> 属性
Company.java
package com.hyxy.po; import java.util.List; public class Company { private int cId; private String cName; private List<Project> list;//实现Company关联Project 一对多 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语句,为了区分多个映射文件,使用命名空间+id进行区分。namespace命名空间--> <mapper namespace="com.hyxy.dao.CompanyDao"> <!--自定义结果映射--> <resultMap id="resultMap" type="com.hyxy.po.Company"> <!--如果数据库中有主键,写id映射--> <id column="companyid" property="cId"></id> <result column="companyname" property="cName"></result> <!--一对多关系映射 (全类名.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; //接口绑定,动态查询,关联关系查询 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(); //一对多 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(); } } }
运行结果:
一对一关联使用<association>,一对多关联使用<collection>
三、Mybatis子查询方式实现关联关系查询
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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