2019/12/15 ~ 16：黑马Mybatis学习笔记（五）—— 多表查询
新建表account
其中用户和账户是一对多的关系
新建实体类Account
package com.itheima.domain;
import java.io.Serializable;
/**
* 账户实体类
*/
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
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;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
'}';
}
}
新建接口IAccountDao
package com.itheima.dao;
import com.itheima.domain.Account;
import com.itheima.domain.AccountUser;
import java.util.List;
/**
* 账户持久层接口
*/
public interface IAccountDao {
/**
* 查询所有账户信息
* @return
*/
List<Account> findAll();
}
新建映射配置文件IAccountDao.xml
<mapper namespace="com.itheima.dao.IAccountDao">
<select id="findAll" resultType="Account">
select * from account
select>
mapper>
新建测试类
package com.itheima.test;
import com.itheima.dao.IAccountDao;
import com.itheima.domain.Account;
import com.itheima.domain.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 AccountTest {
private InputStream in;
private SqlSession sqlSession;
private IAccountDao accountDao;
@Before //用于在测试方法执行之前执行
public void init()throws Exception{
//1.读取配置文件，生成字节输入流
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2.获取SqlSessionFactory
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
//3.获取SqlSession对象
sqlSession = factory.openSession(true);
//4.获取dao的代理对象
accountDao = sqlSession.getMapper(IAccountDao.class);
}
@After//用于在测试方法执行之后执行
public void destroy()throws Exception{
//提交事务
//sqlSession.commit();
//6.释放资源
sqlSession.close();
in.close();
}
/**
* 测试查询所有
*/
@Test
public void testFindAll(){
// 执行方法
List<Account> accounts = accountDao.findAll();
for (Account account : accounts) {
System.out.println(account);
}
}
测试一下查询所有方法，成功
实现查询账户信息时同时查询当前账户所属的用户信息（一对一的查询 ）
从表实体应该包含一个主表实体的对象引用，Account实体类中应该有一个User类的引用
package com.itheima.domain;
import java.io.Serializable;
/**
* 账户实体类
*/
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
// 从表实体应该包含一个主表实体的对象引用
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.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;
}
@Override
public String toString() {
return "Account{" +
"id=" + id +
", uid=" + uid +
", money=" + money +
'}';
}
}
/**
* 查询所有账户信息和当前账户所属用户信息
* @return
*/
List<Account> findAll();
重点：
<mapper namespace="com.itheima.dao.IAccountDao">
<resultMap id="accountUserMap" type="account">
<id property="id" column="aid">id>
<result property="uid" column="uid">result>
<result property="money" column="money">result>
<association property="user" column="uid" javaType="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="address" column="address">result>
<result property="sex" column="sex">result>
<result property="birthday" column="birthday">result>
association>
resultMap>
<select id="findAll" resultMap="accountUserMap">
select u.*, a.id as aid, a.uid, a.money from account a, user u where u.id = a.uid
select>
mapper>
查询所有用户信息，同时获取到当前用户下所有账户信息（一对多的查询 ）
主表实体包含从表实体的集合引用，User类中新增Account集合引用
package com.itheima.domain;
import java.io.Serializable;
import java.util.Date;
import java.util.List;
/**
* 用户实体类
*/
public class User implements Serializable{
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
// 一对多关系映射：主表实体包含从表实体的集合引用
private List<Account> accounts;
public List<Account> getAccounts() {
return accounts;
}
public void setAccounts(List<Account> accounts) {
this.accounts = accounts;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", birthday=" + birthday +
", sex='" + sex + '\'' +
", address='" + address + '\'' +
'}';
}
}
IUserDao接口中：
/**
* 查询所有用户信息，同时获取到当前用户下所有账户信息
* @return
*/
List<User> findAll();
映射配置文件IUserDao.xml
<mapper namespace="com.itheima.dao.IUserDao">
<resultMap id="userAccount" type="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="birthday" column="birthday">result>
<result property="sex" column="sex">result>
<result property="address" column="address">result>
<collection property="accounts" ofType="Account">
<id property="id" column="aid">id>
<result property="uid" column="uid">result>
<result property="money" column="money">result>
collection>
resultMap>
<select id="findAll" resultMap="userAccount">
select * from user u left outer join account a on u.id=a.uid
select>
mapper>
测试类：
/**
* 测试查询所有
*/
@Test
public void findAll(){
List<User> users = userDao.findAll();
for (User user : users) {
System.out.println("---------------------------");
System.out.println(user);
System.out.println(user.getAccounts());
}
}
多对多查询
新建角色表role
新建角色和用户的中间表role_user
并且新建实体类Role，接口IRoleDao，映射配置文件IRoleDao.xml，测试类RoleTest
注意：Role的属性名和数据库属性名不同，User属性名和数据库中的属性名相同
项目结构：
查询所有角色信息同时查询出该角色对应的所有用户信息
SQL语句：
SELECT u.*,r.`ID` AS rid, r.role_name,r.role_desc FROM role r
LEFT OUTER JOIN user_role ur ON r.id = ur.rid
LEFT OUTER JOIN USER u ON ur.uid = u.id;
sql语句查询结果
使用两次左外连接：
IRoleDao接口中定义方法：
/**
* 查询所有角色,同时查询该角色的所有用户信息
* @return
*/
List<Role> findAll();
IRoleDao.xml中配置：
<mapper namespace="com.itheima.dao.IRoleDao">
<resultMap id="roleMap" type="Role">
<id property="roleId" column="rid">id>
<result property="roleName" column="role_name">result>
<result property="roleDesc" column="role_desc">result>
<collection property="users" ofType="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="birthday" column="birthday">result>
<result property="sex" column="sex">result>
<result property="address" column="address">result>
collection>
resultMap>
<select id="findAll" resultMap="roleMap">
SELECT u.*,r.`ID` AS rid, r.role_name,r.role_desc FROM role r
LEFT OUTER JOIN user_role ur ON r.id = ur.rid
LEFT OUTER JOIN USER u ON ur.uid = u.id;
select>
mapper>
测试类RoleTest中：
package com.itheima.test;
import com.itheima.dao.IRoleDao;
import com.itheima.domain.Role;
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 RoleTest {
private InputStream in;
private SqlSession sqlSession;
private IRoleDao roleDao;
@Before
public void init() throws IOException {
// 1.读取配置文件生成字节输入流
in = Resources.getResourceAsStream("SqlMapConfig.xml");
// 2.获取SqlSessionFactory
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
// 3.获取SqlSession
sqlSession = factory.openSession();
// 4.生成代理对象
roleDao = sqlSession.getMapper(IRoleDao.class);
}
@After
public void destroy() throws IOException {
// 释放资源
sqlSession.close();
in.close();
}
@Test
public void testFindAll(){
List<Role> roles = roleDao.findAll();
for (Role role : roles) {
System.out.println("--------------------------------");
System.out.println(role);
System.out.println(role.getUsers());
}
}
}
执行findAll方法：
查询所有用户信息同时查询出该用户对应的所有角色信息
依葫芦画瓢，先定义好sql语句
SELECT u.*,r.`ID` AS rid, r.role_name,r.role_desc FROM USER u
LEFT OUTER JOIN user_role ur ON u.id = ur.uid
LEFT OUTER JOIN role r ON ur.rid = r.id;
查询结果
IUserDao接口中
/**
* 查询所有用户信息同时查询出该用户对应的所有角色信息
* @return
*/
List<User> findAll();
IUserDao.xml配置文件中
<mapper namespace="com.itheima.dao.IUserDao">
<resultMap id="userMap" type="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="birthday" column="birthday">result>
<result property="sex" column="sex">result>
<result property="address" column="address">result>
<collection property="roles" ofType="Role">
<id property="roleId" column="rid">id>
<result property="roleName" column="role_name">result>
<result property="roleDesc" column="role_desc">result>
collection>
resultMap>
<select id="findAll" resultMap="userMap">
SELECT u.*,r.`ID` AS rid, r.role_name,r.role_desc FROM USER u
LEFT OUTER JOIN user_role ur ON u.id = ur.uid
LEFT OUTER JOIN role r ON ur.rid = r.id;
select>
mapper>
测试
/**
* 测试查询所有
*/
@Test
public void findAll(){
List<User> users = userDao.findAll();
for (User user : users) {
System.out.println("---------------------------");
System.out.println(user);
System.out.println(user.getRoles());
}
}
