QueryWrapper、LambdaQueryWrapper以及LambdaQueryChainWrapper用法

1、QueryWrapper

.like("email", "24252") //email对应数据库中列名

    
    
      
      
      
      

   /**
      * 条件构造器 查询操作
      */
     @Test
     void TestQueryWrapperSelect() {
         //1、条件用法
         List<User> userList = userMapper.selectList(new QueryWrapper<User>()
                 .like("email", "24252")
                 .between("age", 20, 22)
                 .or()
                 .eq("name", "zcx")
         );
         System.out.println("userList:" + userList);
     //2、排序用法
     List<User> users = userMapper.selectList(new QueryWrapper<User>()
             .eq("nick_name", "xx")
             .orderByAsc("age")  //升序

// .orderByDesc(“age”) //降序
.last(“limit 0,3”) //last用法：在sql末尾添加sql语句，有sql注入风险
);
System.out.println(“users:”+users);

 }

2、LambdaQueryWrapper

queryWrapper.eq(User::getName,"liangd1"); //可以通过Lambda获取数据库列名

 
 
   
   
   
   

     @Test
     void TestLambdaQueryWrapper() {
         //1、查询单条
         LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
         queryWrapper.eq(User::getName,"liangd1");
         User selectOne = userMapper.selectOne(queryWrapper);
         System.out.println(selectOne);
     //2、查询list以及统计条数
     queryWrapper.eq(User::getName, "zcx");
     List<User> userList = userMapper.selectList(queryWrapper);
     System.out.println("userList:" + userList);
     Integer result = userMapper.selectCount(queryWrapper);
     System.out.println("result:" + result);
 }

3、LambdaQueryChainWrapper

//链式查询方式
User one = new LambdaQueryChainWrapper<>(userMapper)
                 .eq(User::getName, "liangd1")
                 .one();

 
 
   
   
   
   

     @Test
     void TestLambdaQueryChainWrapper() {
         //1、eq查询单条
         User one = new LambdaQueryChainWrapper<>(userMapper)
                 .eq(User::getName, "liangd1")
                 .one();
         System.out.println("UserOne:" + one);
     //2、查询list
     List<User> users = new LambdaQueryChainWrapper<>(userMapper)
             .eq(User::getName, "zcx")
             .list();
     System.out.println("UserList:" + users);

     //3、模糊查询
     List<User> LikeList = new LambdaQueryChainWrapper<>(userMapper)
             .like(User::getEmail, "test")
             .list();
     System.out.println("LikeUser:" + LikeList);
 }