day03-Mybatis中一对一、一对多、多对多查询
2024-09-01 20:22:42
一对一查询
一对一的表结构：
my_account表：
my_user表：
一对一是互相的，A可以找到B，B也可以找到A，方法是一样的，这里就只写一个方向的
通过my_count表找到my_user表的对应元素
实际意义：一个账户（银行卡）只能被一个用户拥有
方法一（最常用）：在Account实体类包含一个User类型对象的引用
Account实体类：
package com.zyb.pojo; import java.io.Serializable;
import java.util.List; public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
//包含另一个对象的引用
private User user; public Account() {
} @Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
", user=" + user +
'}';
} public Integer getId() {
return id;
} public void setId(Integer id) {
this.id = id;
} public Integer getUid() {
return uid;
} public void setUid(Integer uid) {
this.uid = uid;
} public Double getMoney() {
return money;
} public void setMoney(Double money) {
this.money = money;
} }
User实体类：
package com.zyb.pojo; import java.util.Date;
import java.util.List; public class User { private int uid;
private String uname;
private Date birthday;
private String userSex;
private String userAddress; public User() {
} public User(int uid, String uname, Date birthday, String userSex, String userAddress) {
this.uid = uid;
this.uname = uname;
this.birthday = birthday;
this.userSex = userSex;
this.userAddress = userAddress;
} @Override
public String toString() {
return "User{" +
"uid=" + uid +
", uname='" + uname + '\'' +
", birthday=" + birthday +
", userSex='" + userSex + '\'' +
", userAddress='" + userAddress + '\'' +
'}';
} public int getUid() {
return uid;
} public void setUid(int uid) {
this.uid = uid;
} public String getUname() {
return uname;
} public void setUname(String uname) {
this.uname = uname;
} public Date getBirthday() {
return birthday;
} public void setBirthday(Date birthday) {
this.birthday = birthday;
} public String getUserSex() {
return userSex;
} public void setUserSex(String userSex) {
this.userSex = userSex;
} public String getUserAddress() {
return userAddress;
} public void setUserAddress(String userAddress) {
this.userAddress = userAddress;
}
}
AccountMapper.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"> <mapper namespace="com.zyb.dao.AccountDao">
<resultMap id="accountUserMap" type="com.zyb.pojo.Account">
<!--这里写account_id是因为id重名在SQL语句中起的别名-->
<id property="id" column="account_id"></id>
<result property="uid" column="uid"></result>
<result property="money" column="money"></result>
<!-- 一对一关系映射配置user的-->
<!-- 下面property是user是因为在Account实体类User类型变量名是user
第二个javaType是user是因为我给User实体类在mybatis-config.xml起了别名
-->
<association property="user" javaType="user">
<!--主键字段对应-->
<id property="uid" column="id"></id>
<!-- 非主键属性对应-->
<result property="uname" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="userSex" column="sex"></result>
<result property="userAddress" column="address"></result>
</association>
</resultMap>
<select id="selAllAccount" resultType="com.zyb.pojo.Account">
select * from my_account
</select>
<!-- 通过书写Account的子类完成一对多-->
<!-- <select id="selAllAccount2User" resultType="com.zyb.pojo.AccountUser" >-->
<!-- select a.*,u.username,u.address from my_account a,my_user u where a.uid=u.id;-->
<!-- </select>--> <select id="selAllAccount2User" resultType="com.zyb.pojo.Account" resultMap="accountUserMap" >
select u.*,a.id as account_id,a.money,a.uid from my_user u,my_account a where a.UID=u.id
</select> </mapper>
测试类：
package com.zyb.test; import com.zyb.dao.AccountDao;
import com.zyb.pojo.Account;
import com.zyb.pojo.AccountUser;
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 org.junit.After;
import org.junit.Before;
import org.junit.Test; import java.io.IOException;
import java.io.InputStream;
import java.util.List; public class AccountTst { InputStream in;
SqlSession session;
AccountDao accountDao; @Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("mybatis-config.xml");
//2.创建SqlSessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//3.使用工厂生产SqlSession对象
session = factory.openSession();
//4.使用SqlSession创建Dao接口的代理对象
accountDao = session.getMapper(AccountDao.class);
} @After
public void destory() throws IOException {
//session.commit();
//6.释放资源
session.close();
in.close(); } @Test
public void testSelAllAccount(){
List<Account> accounts = accountDao.selAllAccount();
accounts.forEach(x-> System.out.println(x));
} @Test
public void testSelAllAccount2User(){
List<Account> accountUsers=accountDao.selAllAccount2User();
accountUsers.forEach(x-> System.out.println(x));
} }
方法二：建立一个中间类（属性包含需要查询User类的属性）继承Account之后，之后返回一个中间类型的列表就ok了
中间类：
package com.zyb.pojo;
public class AccountUser extends Account{
private String username;
private String address;
public AccountUser() {
}
@Override
public String toString() {
return super.toString()+"AccountUser{" +
"username='" + username + '\'' +
", address='" + address + '\'' +
'}';
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
AccountMapper.xml中的SQL语句以及配置就是上面注释的那个
测试文件将
换成
不细说这个了，不常用。
一对多查询
需要用到的表：my_user、my_account
实际意义：一个用户可以有多个账户（银行卡）
思路：通过上面的一对一，这个思路应该就不是很难想，那就是用户（User）包含一个属于自己账户集合的引用
user实体类：
与上面比就多了一个
UserMapper.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"> <mapper namespace="com.zyb.dao.UserDao">
<!-- 返回类型可以写成user是因为我在mybatis-config.xml已经声明了，否则得写全限定类名-->
<resultMap id="userMap" type="user">
<!--主键字段对应-->
<id property="uid" column="id"></id>
<!-- 非主键属性对应-->
<result property="uname" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="userSex" column="sex"></result>
<result property="userAddress" column="address"></result>
<!-- 这里写accounts是因为在User中List<Account>的变量名为accounts-->
<collection property="accounts" ofType="com.zyb.pojo.Account">
<!-- aid是列名重复SQl语句起别名的缘故-->
<id property="id" column="aid"></id>
<result property="uid" column="uid"></result>
<result property="money" column="money"></result>
</collection>
</resultMap>
<sql id="defaultSql">
select * from my_user
</sql>
<select id="selAll" resultType="User" resultMap="userMap">
select u.*,a.id as aid,a.uid,a.money from my_user u left outer join my_account a on a.uid=u.id
<!--根据id查询一个人-->
</select>
<select id="selOne" resultType="USER" resultMap="userMap" parameterType="int">
<include refid="defaultSql"></include>
where id=#{uid};
</select> </mapper>
测试类：
package com.zyb.test; import com.zyb.dao.UserDao;
import com.zyb.pojo.User;
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 org.junit.After;
import org.junit.Before;
import org.junit.Test; import java.io.IOException;
import java.io.InputStream;
import java.util.List; public class TestUnit { InputStream in;
SqlSession session;
UserDao userDao; @Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("mybatis-config.xml");
//2.创建SqlSessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//3.使用工厂生产SqlSession对象
session = factory.openSession();
//4.使用SqlSession创建Dao接口的代理对象
userDao = session.getMapper(UserDao.class);
} @After
public void destory() throws IOException {
//session.commit();
//6.释放资源
session.close();
in.close(); } @Test
public void testSelAll(){
List<User>users= userDao.selAll();
for(User user:users){
System.out.println("----------------------------------------");
System.out.println(user);
System.out.println(user.getAccounts());
System.out.println("************************************************");
} } @Test
public void testSelOne(){
User user = userDao.selOne(52); System.out.println(user); } }
测试结果：老王有两个账户，传智播客有一个，其它都是空
多对多查询
需要用到的表：my_user、my_role、role_user
思路：互相包含对方类型的的集合
实际意义：一个人扮演多个角色（儿子、父亲、学生），一个角色被多个人扮演
my_role:
user_role（中间表）:
注意：这里的uid与my_user表的id相关联，rid与my_role的id相关联
Role实体类：
package com.zyb.pojo; import java.io.Serializable;
import java.util.List; public class Role implements Serializable {
private Integer roleId;
private String roleName;
private String roleDesc;
private List<User> users; public Role() {
} public List<User> getUsers() {
return users;
} public void setUsers(List<User> users) {
this.users = users;
} @Override
public String toString() {
return "Role{" +
"roleId=" + roleId +
", roleName='" + roleName + '\'' +
", roleDesc='" + roleDesc + '\'' +
'}';
} public Integer getRoleId() {
return roleId;
} public void setRoleId(Integer roleId) {
this.roleId = roleId;
} public String getRoleName() {
return roleName;
} public void setRoleName(String roleName) {
this.roleName = roleName;
} public String getRoleDesc() {
return roleDesc;
} public void setRoleDesc(String roleDesc) {
this.roleDesc = roleDesc;
}
}
User实体类：
package com.zyb.pojo; import java.util.Date;
import java.util.List; public class User { private int uid;
private String uname;
private Date birthday;
private String userSex;
private String userAddress;
//一对多映射
//主表应该包含从表对象集合的引用
//之后collection的property属性填roles
private List<Role> roles; public List<Role> getRoles() {
return roles;
} public void setRoles(List<Role> roles) {
this.roles = roles;
} public User() {
} public User(int uid, String uname, Date birthday, String userSex, String userAddress) {
this.uid = uid;
this.uname = uname;
this.birthday = birthday;
this.userSex = userSex;
this.userAddress = userAddress;
} @Override
public String toString() {
return "User{" +
"uid=" + uid +
", uname='" + uname + '\'' +
", birthday=" + birthday +
", userSex='" + userSex + '\'' +
", userAddress='" + userAddress + '\'' +
'}';
} public int getUid() {
return uid;
} public void setUid(int uid) {
this.uid = uid;
} public String getUname() {
return uname;
} public void setUname(String uname) {
this.uname = uname;
} public Date getBirthday() {
return birthday;
} public void setBirthday(Date birthday) {
this.birthday = birthday;
} public String getUserSex() {
return userSex;
} public void setUserSex(String userSex) {
this.userSex = userSex;
} public String getUserAddress() {
return userAddress;
} public void setUserAddress(String userAddress) {
this.userAddress = userAddress;
}
}
UserMapper.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"> <mapper namespace="com.zyb.dao.UserDao">
<!-- 返回类型可以写成user是因为我在mybatis-config.xml已经声明了，否则得写全限定类名-->
<resultMap id="userMap" type="user">
<!--主键字段对应-->
<id property="uid" column="id"></id>
<!-- 非主键属性对应-->
<result property="uname" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="userSex" column="sex"></result>
<result property="userAddress" column="address"></result>
<collection property="roles" ofType="com.zyb.pojo.Role">
<id property="roleId" column="rid"></id>
<result property="roleName" column="role_name"></result>
<result property="roleDesc" column="role_desc"></result>
</collection> </resultMap>
<sql id="defaultSql">
select * from my_user
</sql>
<select id="selAll" resultMap="userMap">
select u.*,r.ROLE_NAME,r.ROLE_DESC,r.ID as rid from my_user u
left outer join user_role ur
on u.id=ur.UID
left outer join my_role r
on r.ID=ur.RID
<!--根据id查询一个人-->
</select>
<select id="selOne" resultType="USER" resultMap="userMap" parameterType="int">
<include refid="defaultSql"></include>
where id=#{uid};
</select> </mapper>
RoleMapper.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">
<mapper namespace="com.zyb.dao.RoleDao"> <resultMap id="roleMap" type="com.zyb.pojo.Role">
<!-- 因为有两个id所以在查询结果重命名了id-->
<!-- select u.*,r.ROLE_NAME,r.ROLE_DESC,r.ID as rid-->
<id property="roleId" column="rid"></id>
<result property="roleName" column="role_name"></result>
<result property="roleDesc" column="role_desc"></result>
<!-- collection中的property是包含集合的名字-->
<collection property="users" ofType="user">
<!--主键字段对应-->
<id property="uid" column="id"></id>
<!-- 非主键属性对应-->
<result property="uname" column="username"></result>
<result property="birthday" column="birthday"></result>
<result property="userSex" column="sex"></result>
<result property="userAddress" column="address"></result>
</collection>
</resultMap>
<select id="selAll" resultMap="roleMap">
select u.*,r.ROLE_NAME,r.ROLE_DESC,r.ID as rid from
my_role r left outer join user_role ur
on r.ID=ur.RID
left outer join my_user u
on ur.UID=u.id
</select> </mapper>
测试类大同小异就不写了
运行结果：
}
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