Mybatis（19）注解实现多表查询

两个类，User，Account

查询每个账户以及其对应的用户信息，一对一查询，采用及时加载

Account类

package com.itheima.domain;import java.io.Serializable;public class Account implements Serializable {private Integer id;private Integer uid;private Double money;//多对一（mybatis中称之为一对一）的映射，一个账户只能属于一个用户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;}@Overridepublic String toString() {return "Account{" +"id=" + id +", uid=" + uid +", money=" + money +", user=" + user +'}';}
}

User类

public class User implements Serializable {private Integer userId;private String userName;private String userAddress;private String userSex;private Date userBirthday;//加入get和set方法
}

IAccountDao接口

public interface IAccountDao {/**查询所有账户，并且获取每个账户所属的用户信息**/@Select("select * from account")@Results(id="accountMap",value = {@Result(id=true,column = "id",property = "id"),@Result(column = "uid",property = "uid"),@Result(column = "money",property = "money"),@Result(column = "uid",property = "user",one =@One(select = "com.itheima.dao.IUserDao.findById",fetchType = FetchType.EAGER))})List<Account> findAll();/**根据用户id查询账户信息**/@Select("select * from account where uid=#{uid}")List<Account> finAccountByUid(Integer userId);
}

验证：

@Testpublic void testFindAll(){List<Account> accounts=accountDao.findAll();for(Account account:accounts){System.out.println("每个账户信息");System.out.println(account);System.out.println(account.getUser());}}

结果：

Account{id=3, uid=46, money=2000.0, user=User{userId=46, userName='老王', userAddress='北京', userSex='女', userBirthday=Wed Mar 07 17:37:26 CST 2018, accounts=[Account{id=1, uid=46, money=1000.0, user=null}, Account{id=3, uid=46, money=2000.0, user=null}]}}
User{userId=46, userName='老王', userAddress='北京', userSex='女', userBirthday=Wed Mar 07 17:37:26 CST 2018, accounts=[Account{id=1, uid=46, money=1000.0, user=null}, Account{id=3, uid=46, money=2000.0, user=null}]}

实现一对多查询，每个用户以及对应的账户信息

User类

public class User implements Serializable {private Integer userId;private String userName;private String userAddress;private String userSex;private Date userBirthday;//一对多关系映射，一个用户对应多个账户private List<Account> accounts;public List<Account> getAccounts() {return accounts;}public void setAccounts(List<Account> accounts) {this.accounts = accounts;}public Integer getUserId() {return userId;}public void setUserId(Integer userId) {this.userId = userId;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getUserAddress() {return userAddress;}public void setUserAddress(String userAddress) {this.userAddress = userAddress;}public String getUserSex() {return userSex;}public void setUserSex(String userSex) {this.userSex = userSex;}public Date getUserBirthday() {return userBirthday;}public void setUserBirthday(Date userBirthday) {this.userBirthday = userBirthday;}@Overridepublic String toString() {return "User{" +"userId=" + userId +", userName='" + userName + '\'' +", userAddress='" + userAddress + '\'' +", userSex='" + userSex + '\'' +", userBirthday=" + userBirthday +", accounts=" + accounts +'}';}
}

IUserDao接口：

public interface IUserDao {/*查询所有用户*/@Select("select * from user")@Results(id = "userMap",value = {@Result(id=true,column = "id",property = "userId"),@Result(column = "username",property = "userName"),@Result(column = "address",property = "userAddress"),@Result(column = "sex",property = "userSex"),@Result(column = "birthday",property = "userBirthday"),@Result(column ="id",property = "accounts",many = @Many(select = "com.itheima.dao.IAccountDao.finAccountByUid",fetchType = FetchType.LAZY))})List<User> findAll();/*查询一个用户*/@Select("select * from user where id=#{id}")@ResultMap(value = {"userMap"})User findById(Integer userId);/*根据用户名称模糊查询*/@Select("select * from user where username like #{username}")@ResultMap(value = {"userMap"})List<User> findUserByName(String username);
}

验证：

@Testpublic void testFindAllUser(){List<User> users=userDao.findAll();for (User user:users){System.out.println("每个用户的账户信息");System.out.println(user);System.out.println(user.getAccounts());}}

结果：

User{userId=46, userName='老王', userAddress='北京', userSex='女', userBirthday=Wed Mar 07 17:37:26 CST 2018, accounts=[Account{id=1, uid=46, money=1000.0, user=null}, Account{id=3, uid=46, money=2000.0, user=null}]}
[Account{id=1, uid=46, money=1000.0, user=null}, Account{id=3, uid=46, money=2000.0, user=null}]

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