Linq-常用的方法

往集合中填充一些基础数据

class Program
    {
        static void Main(string[] args)
        {
            List<Employee> list = new()
            {
                new Employee { Id = 1, Name = "Hpf", Age = 38, Gender = true, Salary 
= 1000 },
                new Employee { Id = 2, Name = "Jim", Age = 15, Gender = true, Salary 
= 2000 },
                new Employee { Id = 3, Name = "Lily", Age = 27, Gender = false, 
Salary = 1500 },
                new Employee { Id = 4, Name = "Kimi", Age = 15, Gender = true, 
Salary = 2700 },
                new Employee { Id = 5, Name = "Nancy", Age = 38, Gender = false, 
Salary = 3200 },
                new Employee { Id = 6, Name = "Jack", Age = 21, Gender = false, 
Salary = 4400 },
                new Employee { Id = 7, Name = "Zack", Age = 38, Gender = true, 
Salary = 7500 }
            };

            Console.ReadLine();
        }
    }
}

1.Count() 获取数据条数

list.Count(it => it.Age > 18 && it.Salary > 5000);

2.Any() 是否至少有一条数据

bool B = list.Any(it => it.Salary > 8000)

3.Single 有且只有一条满足要求的数据

多条满足条件或一条也没有，此方法会报错

Employee e =  list.Single(it => it.Name=="Hpf");
Console.WriteLine(e == null);

4.SingleOrDefault 最多有一条满足要求的数据

多条满足条件，此方法会报错；没有数据则返回数据类型的默认值

int[] nums = new int[] {3,4,8};
int i = nums.SingleOrDefault(it => it>10);
Console.WriteLine(i);

-- OutPut 0

5.First 至少有一条，返回第一条

一条也没有，此方法会报错

6.FirstOrDefault 返回第一条或默认值

7.OrderBy() 对数据正序排序

list.OrderBy(it => it.Age>18);

8.OrderByDescending() 倒序排序

list.OrderByDescending(it => it.Age>18);

9.ThenBy()、ThenByDescending() 多规则排序

list.OrderBy(it => it.Age>18).ThenBy(it => it.Salary);

10.Skip(n)、Take(n) 限制结果集，获取部分数据

-- 从第二条数据开始，获取三条数据
list.Skip(2).Take(3);