Mybatis入门笔记(14)——基于注解开发一对多的查询配置

需求：使用注解方式实现，查询用户信息时，也要查询对应的账户列表。

一个用户具有多个账户信息，所以形成了用户(User)与账户(Account)之间的一对多关系。

1. User实体类中加入List<Account>

   package com.ben.domain;
   
   import java.io.Serializable;
   import java.util.Date;
   import java.util.List;
   
   /**
    * @ClassName: User
    * @author: benjamin
    * @version: 1.0
    * @description: TODO
    * @createTime: 2019/07/19/21:43
    */
   
   public class User implements Serializable {
       private int id;
       private String username;// 用户姓名
       private String sex;// 性别
       private Date birthday;// 生日
       private String address;// 地址
       
    	//一对多关系映射：主表方法应该包含一个从表方的集合引用。
       private List<Account> accounts;
   
       public List<Account> getAccounts() {
           return accounts;
       }
   
       public void setAccounts(List<Account> accounts) {
           this.accounts = accounts;
       }
   
       public int getId() {
           return id;
       }
   
       public void setId(int id) {
           this.id = id;
       }
   
       public String getUsername() {
           return username;
       }
   
       public void setUsername(String username) {
           this.username = username;
       }
   
       public String getSex() {
           return sex;
       }
   
       public void setSex(String sex) {
           this.sex = sex;
       }
   
       public Date getBirthday() {
           return birthday;
       }
   
       public void setBirthday(Date birthday) {
           this.birthday = birthday;
       }
   
       public String getAddress() {
           return address;
       }
   
       public void setAddress(String address) {
           this.address = address;
       }
   
       @Override
       public String toString() {
           return "User [id=" + id + ", username=" + username + ", sex=" + sex
                   + ", birthday=" + birthday + ", address=" + address + "]";
       }
   }
   

2. 编写用户的持久层接口并使用注解配置

   /**
   * @Description: 查询所有用户
   * @Param:
   * @return:
   * @Author: benjamin
   * @Date: 2019/7/19
   */
   @Select("select * from user")
   @Results(id="userMap",
           value = {
                   @Result(id=true,column = "id",property = "id"),
                   @Result(column = "username", property = "username"),
                   @Result(column = "sex", property = "sex"),
                   @Result(column = "address", property = "address"),
                   @Result(column = "birthday", property = "birthday"),
                   @Result(column = "id", property = "accounts",
                           many = @Many(
                                   select = "com.ben.dao.IAccountDao.findAccountById",
                                   fetchType = FetchType.LAZY
                           )
                   )
           })
   List<User> findAll();
   

3. 编写账户的持久层接口并使用注解配置

   /**
    * @Description: 根据用户ID查询用户下的所有账户
    * @Param:
    * @return:
    * @Author: benjamin
    * @Date: 2019/7/20
    */
   @Select("select * from account where uid = #{id}")
   List<Account> findAccountByID(Integer userId);
   

4. 编写测试方法

   //测试查询所有
   @Test
   public void testFindAll(){
       List<User> users = userDao.findAll();
       for(User user : users){
           System.out.println("----每个用户拥有不止一个账户----");
           System.out.println(user);
           System.out.println(user.getAccounts());
       }
   }