使用resultMap实现高级结果映射

Java 2020-09-16

使用resultMap实现高级结果映射

resultMap的属性:

1.属性

id：resultMap的唯一标识。
type：resulMap的映射结果类型（一般为Java实体类）。
2.子节点

id：一般对应数据库的主键 id，设置此项可以提升数据库性能。
result：映射到JavaBean的某个 “ 简单类型 ” 属性，如基础数据类型，包装类等。子节点 id 和 result 均可以实现最基本的结果集映射，将列映射到简单数据类型的属性。。这两者唯一不同的是：在比较对象实例时 id 将作为结果集的标识属性。这有助于提高总体性能，特别是应用缓存的嵌套结果映射的时候，若需要实现高级结果映射，就需要下面两个配置项：association 和 collection
association（仅处理一对一的关联关系）

<resultMap type="User" id="userRoleResult">
　　<id property="id" column="id"/>
　　<result property="userName" column="userName"/>
　　<association property="role" javaType="Role">
　　　　<id property="roleName" column="roleName"/>
　　</association>
</resultMap>

javaType：完整java类名或者别名。若映射到一个JavaBean，则MyBatis通常会自行检测到其类型；若映射到一个HashMap，则应该明确指定javaType，类确保所需行为。此处为Role。
property：映射到数据库列的实体对象的属性，此处为在User实体类里定义的JavaBean对象属性（role）。association的子元素如下：
id。
result。
property：映射到数据库列的实体类对象的属性。此处为Role的属性。
column：数据库列名或者别名。
在做结果映射的过程中，要确保所有的列名都是唯一无歧义的。

collection（属性是一个集合列表）

<resultMap type="User" id="userRoleResult">
　　<id property="id" column="id"/>
　　<result property="userName" column="userName"/>
　　<collection property="List" ofType="Address">
　　　　<id property="id" column="id"/>
　　　　<result property="postCode" column="postCode"/>
　　</collection>
</resultMap>

ofType：完整java类名或者别名，即集合所包含的类型，此处为Address。
property：映射数据库列的实体类对象的属性。此处为在User里定义的属性：List（可以理解为一个名为List，元素类型为Address的ArrayList集合）
collection的子元素与association基本一致。

一对多

实体
package com.smbms.entity; import java.math.BigInteger; import java.util.Date; import java.util.List; /** * 角色 */


public class SmbmsRole {　　　　　　　　　　　　　　
    private Integer rid;
    private String roleCode;
    private String roleName;
    private BigInteger createdBy;
    private Date creationDate;
    private BigInteger modifyBy;
    private Date modifyDate;

    //植入多的一方      集合
    private List<SmbmsUser> userList;

    public List<SmbmsUser> getUserList() {
        return userList;
    }

    public void setUserList(List<SmbmsUser> userList) {
        this.userList = userList;
    }

    public Integer getRid() {
        return rid;
    }

    public void setRid(Integer rid) {
        this.rid = rid;
    }

    public String getRoleCode() {
        return roleCode;
    }

    public void setRoleCode(String roleCode) {
        this.roleCode = roleCode;
    }

    public String getRoleName() {
        return roleName;
    }

    public void setRoleName(String roleName) {
        this.roleName = roleName;
    }

    public BigInteger getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(BigInteger createdBy) {
        this.createdBy = createdBy;
    }

    public Date getCreationDate() {
        return creationDate;
    }

    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }

    public BigInteger getModifyBy() {
        return modifyBy;
    }

    public void setModifyBy(BigInteger modifyBy) {
        this.modifyBy = modifyBy;
    }

    public Date getModifyDate() {
        return modifyDate;
    }

    public void setModifyDate(Date modifyDate) {
        this.modifyDate = modifyDate;
    }
}

　DAO层


package com.smbms.dao;

import com.smbms.entity.SmbmsUser;

import java.util.List;

public interface ISmbmsUserDao {
    //查询所有用户信息  包含角色信息
    public List<SmbmsUser> getUserList();
}

　DAO层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">
<!--namespace需要指向接口全路径-->
<mapper namespace="com.smbms.dao.ISmbmsRoleDao">
    <resultMap id="roleAndUserMapper" type="SmbmsRole">
        <id column="rid" property="rid"></id>
        <result column="roleName" property="roleName"/>
        <!--映射多的一方 property代表实体当中多的一方的属性名      ofType代表集合当中泛型类型-->
        <!-- select 代表执行查询的ID   column所引用的条件列   -->
        <collection property="userList" ofType="SmbmsUser" select="getRoleAndUserMutilsql" column="rid">

        </collection>
    </resultMap>
    
    <!--写成一条sql-->
    <select id="getRoleAndUser" resultMap="roleAndUserMapper">
        select u.id,u.userName,u.userRole,r.rid,r.roleName from smbms_user as u,smbms_role as r where u.userRole=r.rid and r.rid=#{id}
    </select>
    <!--写成两条sql-->
    <select id="getRoleAndUser" resultMap="roleAndUserMapper">
        select * from  smbms_role where rid=#{id}
    </select>
    <select id="getRoleAndUserMutilsql" resultType="SmbmsUser">
        select * from  smbms_user where userRole=#{rid}
    </select>
</mapper>

测试

package com.smbms.test;

import com.smbms.dao.ISmbmsRoleDao;
import com.smbms.entity.SmbmsRole;
import com.smbms.entity.SmbmsUser;
import com.smbms.util.MybatisUtil;
import org.apache.ibatis.session.sqlSession;
import org.junit.Test;

public class CollectionTest {
    @Test
    public void getRoleAndUsertest(){
        sqlSession sqlSession = MybatisUtil.getsqlSession();
        ISmbmsRoleDao mapper = sqlSession.getMapper(ISmbmsRoleDao.class);


        SmbmsRole role = mapper.getRoleAndUser(3);
        System.out.println("角色："+role.getRoleName());
        for(SmbmsUser user : role.getUserList()){
            System.out.print("\t用户："+user.getUserName());
        }
    }
}

多对一　

实体

 

package com.smbms.entity;


import java.math.BigInteger;
import java.util.Date;

/**
 *
 */
public class SmbmsUser {
    private Integer id;
    private String userCode;
    private String userName;
    private String userPassword;
    private Integer gender;
    private Date birthday;
    private String phone;
    private String address;
    private Integer userRole;
    private BigInteger createdBy;
    private Date creationDate;
    private BigInteger modifyBy;
    private Date modifyDate;

    //关联一的一方
    private SmbmsRole role;

    public SmbmsRole getRole() {
        return role;
    }

    public void setRole(SmbmsRole role) {
        this.role = role;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUserCode() {
        return userCode;
    }

    public void setUserCode(String userCode) {
        this.userCode = userCode;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getUserPassword() {
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
    }

    public Integer getGender() {
        return gender;
    }

    public void setGender(Integer gender) {
        this.gender = gender;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public Integer getUserRole() {
        return userRole;
    }

    public void setUserRole(Integer userRole) {
        this.userRole = userRole;
    }

    public BigInteger getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(BigInteger createdBy) {
        this.createdBy = createdBy;
    }

    public Date getCreationDate() {
        return creationDate;
    }

    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }

    public BigInteger getModifyBy() {
        return modifyBy;
    }

    public void setModifyBy(BigInteger modifyBy) {
        this.modifyBy = modifyBy;
    }

    public Date getModifyDate() {
        return modifyDate;
    }

    public void setModifyDate(Date modifyDate) {
        this.modifyDate = modifyDate;
    }
}






 

　　

 

DAO层

package com.smbms.dao;

import com.smbms.entity.SmbmsUser;

import java.util.List;

public interface ISmbmsUserDao {
    //查询所有用户信息  包含角色信息
    public List<SmbmsUser> getUserList();
}

　　

DAO层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">
<!--namespace需要指向接口全路径-->
<mapper namespace="com.smbms.dao.ISmbmsUserDao">
    <resultMap id="userListAndRole" type="SmbmsUser">
        <id column="id" property="id"></id>
        <result column="userName" property="userName"/>
        <association property="role" javaType="SmbmsRole" select="getRole" column="userRole">
            <id column="rid" property="rid"></id>
            <result column="roleName" property="roleName"/>
        </association>
    </resultMap>

    <!--<select id="getUserList" resultMap="userListAndRole">
        select u.id,smbms_role as r where u.userRole=r.rid
    </select>-->


    <select id="getUserList" resultMap="userListAndRole">
        select * from smbms_user
    </select>
    <select id="getRole" resultType="SmbmsRole">
        select * from smbms_role where rid=#{userRole}
    </select>
</mapper>

　　

测试

package com.smbms.test;

import com.smbms.dao.ISmbmsUserDao;
import com.smbms.entity.SmbmsUser;
import com.smbms.util.MybatisUtil;
import org.apache.ibatis.session.sqlSession;
import org.junit.Test;

import java.util.List;

public class AssociationTest {
    @Test
    public void getUserListtest(){
        sqlSession sqlSession = MybatisUtil.getsqlSession();
        ISmbmsUserDao mapper = sqlSession.getMapper(ISmbmsUserDao.class);


        List<SmbmsUser> userList = mapper.getUserList();
        for(SmbmsUser user:userList){
            System.out.println("用户："+user.getUserName()+"\t角色："+user.getRole().getRoleName());
        }
    }
}

　　

多对多

实体

 

package com.smbms.entity;

import java.util.List;

public class Teacher {
    private Integer tid;
    private String tname;

    //植入学员集合，代表一名教员可以教授多名学员
    private List<Student> students;

    public Integer getTid() {
        return tid;
    }

    public void setTid(Integer tid) {
        this.tid = tid;
    }

    public String getTname() {
        return tname;
    }

    public void setTname(String tname) {
        this.tname = tname;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}




package com.smbms.entity;

import java.util.List;

public class Student {
    private Integer stuid;
    private String stuname;
    private String stuaddress;

    //植入Teacher集合，代表一名学员可以被多名教员教授
    private List<Teacher> teachers;

    public List<Teacher> getTeachers() {
        return teachers;
    }

    public void setTeachers(List<Teacher> teachers) {
        this.teachers = teachers;
    }

    public Integer getStuid() {
        return stuid;
    }

    public void setStuid(Integer stuid) {
        this.stuid = stuid;
    }

    public String getStuname() {
        return stuname;
    }

    public void setStuname(String stuname) {
        this.stuname = stuname;
    }

    public String getStuaddress() {
        return stuaddress;
    }

    public void setStuaddress(String stuaddress) {
        this.stuaddress = stuaddress;
    }
}

 

　　

 

DAO层

package com.smbms.dao;

import com.smbms.entity.Student;

import java.util.List;

public interface IStudentDao {
    //查询所有学生信息  以及授课教员
    public List<Student> getStudentInfo();
}

　　

DAO层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">
<!--namespace需要指向接口全路径-->
<mapper namespace="com.smbms.dao.IStudentDao">
    <resultMap id="studentAndTeacherMapper" type="Student">
        <id column="stuid" property="stuid"/>
        <result column="stuname" property="stuname"/>
        <collection property="teachers" ofType="Teacher">
            <id column="tid" property="tid"></id>
            <result property="tname" column="tname"/>
        </collection>
    </resultMap>
    <select id="getStudentInfo" resultMap="studentAndTeacherMapper">
        select * from student,teacher,stu_t where student.stuid=stu_t.stuid and teacher.tid=stu_t.tid
    </select>
</mapper>

　　

测试

package com.smbms.test;

import com.smbms.dao.IStudentDao;
import com.smbms.entity.Student;
import com.smbms.entity.Teacher;
import com.smbms.util.MybatisUtil;
import org.apache.ibatis.session.sqlSession;
import org.junit.Test;

import java.util.List;

public class ManeyTooManey {
    @Test
    public void getStudentInfo(){
        sqlSession sqlSession = MybatisUtil.getsqlSession();
        IStudentDao mapper = sqlSession.getMapper(IStudentDao.class);

        List<Student> studentInfo = mapper.getStudentInfo();
        for(Student stu:studentInfo){
            System.out.println("学生："+stu.getStuname());
            for (Teacher teacher:stu.getTeachers()){
                System.out.print("\t教员："+teacher.getTname());
            }
            System.out.println();
        }

    }
}

　　

自联接

实体

 

package com.smbms.entity;

import java.util.List;

public class City {
    private Integer cid;
    private String cname;
    private Integer pid;
    //自关联集合     代表的是当前City对象的子集集合
    public List<City> childCitys;

    @Override
    public String toString() {
        return "City{" +
                "cid=" + cid +
                ",cname=‘" + cname + ‘\‘‘ +
                ",pid=" + pid +
                ",childCitys=" + childCitys +
                ‘}‘;
    }

    public List<City> getChildCitys() {
        return childCitys;
    }

    public void setChildCitys(List<City> childCitys) {
        this.childCitys = childCitys;
    }

    public Integer getCid() {
        return cid;
    }

    public void setCid(Integer cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public Integer getPid() {
        return pid;
    }

    public void setPid(Integer pid) {
        this.pid = pid;
    }


}

 

　　

 

DAO层

package com.smbms.dao;

import com.smbms.entity.City;

import java.util.List;

public interface ICityDao {
    //查询河南省  下的所有子集
    public City getCityAndChildCitys(Integer cid);
}

　　

DAO层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">
<!--namespace需要指向接口全路径-->
<mapper namespace="com.smbms.dao.ICityDao">
    <resultMap id="CityAndChildCitysMapper" type="City">
        <id column="cid" property="cid"></id>
        <result column="cname" property="cname"/>
        <result column="pid" property="pid"/>
        <collection property="childCitys" ofType="City" select="getCityAndChildCitysMutilsql" column="cid">
            <id column="cid" property="cid"></id>
            <result column="cname" property="cname"/>
            <result column="pid" property="pid"/>
        </collection>
    </resultMap>

   <select id="getCityAndChildCitys" resultMap="CityAndChildCitysMapper">
       select * from city where cid=#{cid}
   </select>
    <select id="getCityAndChildCitysMutilsql" resultMap="CityAndChildCitysMapper">
       select * from city where pid=#{cid}
   </select>
</mapper>

　　

测试

package com.smbms.test;

import com.smbms.dao.ICityDao;
import com.smbms.entity.City;
import com.smbms.util.MybatisUtil;
import org.apache.ibatis.session.sqlSession;
import org.junit.Test;

public class DGTest {
    @Test
    public void getCityAndChildCitystest(){
        sqlSession sqlSession = MybatisUtil.getsqlSession();
        ICityDao mapper = sqlSession.getMapper(ICityDao.class);

        City city = mapper.getCityAndChildCitys(410000);
        System.out.println(city.toString());
    }
}

相关文章

String真的不可变吗？
Java中的String是不可变对象 在面向对象及函数编程语言中，不...
String, StringBuffer 和 StringBuilder之间的区别
String, StringBuffer 和 StringBuilder 可变性 String不可变...
讲讲Java的序列化反序列化？
序列化：把对象转换为字节序列的过程称为对象的序列化. 反序...
数组到底是不是对象
先说结论，是对象！可以继续往下看 数组是不是对象 什么是对...
金融、支付行业的开发者不得不知道的float、double计算误差问题
为什么浮点数 float 或 double 运算的时候会有精度丢失的风险...
浅谈Integer缓存机制原理
面试题引入 这里引申出一个经典问题，看下面代码 Integer a ...