using System;
using System.Collections.Generic;
using System.Linq;
namespace DeferredExecutionExp
{
  class Program
  {
    static void Main(string[] args)
    {
      List<Student> studentList = new List<Student>()
      {
        new Student(){Id =1, Name="ZhangSan", Age=20},
        new Student(){Id =2, Name=null, Age=21},
        new Student(){Id =3, Name="Lisi", Age=22}
      };
      var queryedStudentList = studentList.Where(it => it.Name.Trim() != "ZhangSan");//(1)
      if (queryedStudentList.Count() > 0)//(2)
      {
        foreach (var student in queryedStudentList)//(3)
        {
          Console.WriteLine(student.Name);
        }
      }
    }
  }
  public class Student
  {
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
  }
}