MyBatis~(贰)

笔记代码
面向接口编程
注解开发
对应关系
- 多对一

笔记代码

面向接口编程

主要目的就是解耦,分层开发中,上层业务不用管具体的实现.
使得 规范 和 实现 两部分分离,接口作为项目骨架.

注解开发

简单上手

接口上直接注解 SQL 语句

public interface UserMapper {
  @Select("select * from mybatis.user")
  List<User> getUsers();
}

绑定接口

<mappers>
  <!--之前是用xml绑定的-->
  <!--<mapper resource="Mappers/UserMapper.xml"/>-->

  <!--这里换成绑定接口-->
  <mapper class="dao.UserMapper"/>
</mappers>

实现原理: 通过反射机制获取接口中的信息,然后用动态代理实现业务.
调试

原理分析

mybatis 的执行流程

CRUD

UserMapper

package dao;

import org.apache.ibatis.annotations.*;
import pojo.User;

import java.util.List;
import java.util.Map;

public interface UserMapper {

  @Select("select * from mybatis.user")
  List<User> getUsers();

  /*
    基本类型的参数或者String类型，需要加上
    引用类型不需要加
    如果只有一个基本类型的话，可以忽略，但是建议都加上
    我们在SQL中引用的就是我们这里的@Param()中设定的属性名
    重要: 这里方法不能重载! 两个同名方法会使MyBatis运行报错(开发时JDK不会报错)
  */
  @Select("select * from mybatis.user where id = #{id}")
  User getUserById(int id);

  // 多个参数的情况下,必须加上@Param注解
  @Select("select * from mybatis.user where id = #{id} and name = #{name}")
  User getUserByIdAndName(@Param("id") int id, @Param("name") String name);

  @Insert("insert into mybatis.user(id,name,pwd) values (#{id},#{name},#{pwd})")
  int addUser(User user);

  //注意SQL格式,set 和 where顺序不能颠倒
  @Update("update mybatis.user set name = #{name},pwd = #{pwd} where id = #{id}")
  int updateUser(User user);

  @Delete("delete from mybatis.user where id = #{id}")
  int deleteUserById(int id);
}

test

package dao;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.MyBatisUtils;

import java.util.List;

public class UserMapperTest {

  @Test
  public void getUsers() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = userMapper.getUsers();
    for (User user : userList) {
      System.out.println(user);
    }
    sqlSession.close();
  }

  @Test
  public void testGetUserById() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    User user = userMapper.getUserById(1);
    System.out.println(user);
    sqlSession.close();
  }

  @Test
  public void getUserById() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    User user = userMapper.getUserByIdAndName(1, "张三");
    System.out.println(user);
    sqlSession.close();
  }

  @Test
  public void addUser() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    int i = userMapper.addUser(new User(7, "七七", "45648"));
    if (i > 0)
      sqlSession.commit();
    sqlSession.close();
  }

  @Test
  public void updateUser() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    int i = userMapper.updateUser(new User(7, "七七", "12345678"));
    if (i > 0)
      sqlSession.commit();
    sqlSession.close();
  }

  @Test
  public void deleteUserById() {
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    if (userMapper.deleteUserById(7) > 0)
      sqlSession.commit();
    sqlSession.close();
  }
}