mybatis第三天及整理

延迟加载，一二级缓存，注解开发完善，以及用注解开发实现延迟加载，一对多，一对一，一二级缓存

一对一

要实现注解开发，首先创建一个普通maven项目，在pom.xml中加入所需的依赖，在数据库中有user和account表，创建两个实体类user和account，放在com.domain包中，两个实体类的字段分别对应数据库表中的列名，配置好sqlMapConfig.xml(别名，环境，映射),在com.dao中创建AccountDao, 如下

 package com.dao;

import com.domain.Account;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;

public interface AccountDao {
    /**
     * 查询用户所有,并且获取每个账户所属的用户信息
     * @return
     */
    @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(property = "user",column = "uid",one = @One(select = "com.dao.UserDao.findById",fetchType = FetchType.EAGER))
    })
    List<Account> findAll();
            //实际开发中，对一的选择直接加载，对多的选择延迟加载

    @Select("select * from account where uid = #{uid}")
    List<Account> findAccountByUid(Integer id);
}

以上就是注解开发，@select对应的就是xml文件映射的select标签，@Results对应的就是ResultMap标签，主键在@Result配置，一对一在于

 @Result(property = "user",column = "uid",one = @One(select = "com.dao.UserDao.findById",fetchType = FetchType.EAGER))

一个账户对应一个用户，one属性中可以配置方法名的映射，要想通过account表中的uid查到user的信息，可以通过UserDao中的方法findById查到user的信息，然后封装至account实体中，所以，account实体中就有添加

//一对一，账户对用户
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

user的get和set,便于封装，再写一个测试类

@Test
    public void   findAll() throws Exception{

        List<Account> accounts =  accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
        }

    }

查询account信息的同时，得到user的信息。

一对多

先在User实体类中添加多的account

//一对多
    private List<Account> accounts;

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

package com.dao;

import com.domain.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;

public interface UserDao {
    /**
     * 注解方式查询所有
     * @return
     */
    @Select("select * from user")
    @Results(id = "userMap",value = {
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "birthday",property = "birthday"),
            @Result(column = "sex",property = "sex"),
            @Result(column = "address",property = "address"),
            @Result(property = "accounts",column = "id",many = @Many(select = "com.dao.AccountDao.findAccountByUid",fetchType = FetchType.LAZY))
    })
    List<User> findAll(); 

    /**
     * 通过id查询用户
     * @param id
     * @return
     */
    @Select("select * from user where id = #{id}")
    User findById(Integer id); 

}

通过和实体类中定义的accounts字段对应，

 @Result(property = "accounts",column = "id",many = @Many(select = "com.dao.AccountDao.findAccountByUid",fetchType = FetchType.LAZY))

通过com.dao.AccountDao.findAccountByUid方法，查询到多的account信息