LINQ使用Contains将属性投影到一个新的匿名类型中
本文关键字:一个 类型 Contains 使用 属性 投影 LINQ | 更新日期: 2024-10-24 06:55:00
我有以下代码,我正在尝试使其工作,但它仍然没有编译。非常感谢。
List<Employee> emploees = new List<Employee>()
{
new Employee { ID = 101, Name = "Rosy" },
new Employee { ID = 102, Name = "Sury" }
};
var result = emploees.Select(x=> new {x.ID, x.Name}).Contains(new Employee { ID = 101, Name = "Rosy" });
Console.WriteLine(result);
首先,您不需要将列表项投影到匿名对象。此外,IMO Any()
比Contains()
:更适合这种情况
var result = emploees.Any(x => x.ID == 101 && x.Name == "Rosy");
如果仍要使用Contains
,则需要为Employee
类创建比较器。
sealed class MyComparer : IEqualityComparer<Employee>
{
public bool Equals(Employee x, Employee y)
{
if (x == null)
return y == null;
else if (y == null)
return false;
else
return x.ID == y.ID && x.Name == y.Name;
}
public int GetHashCode(Employee obj)
{
unchecked
{
int hash = 17;
hash = hash * 23 + obj.ID.GetHashCode();
hash = hash * 23 + obj.Name.GetHashCode();
return hash;
}
}
}
并将您的代码更改为:
var result = emploees.Contains(new Employee { ID = 101, Name = "Rosy" }, new MyComparer());
为什么要投影到匿名类型中,然后进行类型比较检查?
你可以简单地使用Any
来实现你在这里需要的东西:
var result = emploees
.Select(x=> new {x.ID, x.Name})
.Any(x => x.ID == 101 && x.Name == "Rosy");
Console.WriteLine(result);
或者简单地说,没有Select
,因为您只是使用bool
:
bool result = emploees
.Any(x => x.ID == 101 && x.Name == "Rosy");
Console.WriteLine(result);
不过,为了完整起见,如果您真的想要使用Contains
,请重写Employee
类的IEquatable
:
public class Employee : IEquatable<Employee>
{
public bool Equals( Employee other)
{
return this.ID == other.ID &&
this.Name == other.Name;
}
}
然后执行:
var result = emploees
.Select(x => new Employee {x.ID, x.Name})
.Contains(new Employee { ID = 101, Name = "Rosy" });
Console.WriteLine(result);