C# 使用 Linq 搜索对象列表中是否存在值
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Searching if value exists in a list of objects using Linq
提问by Tony_Henrich
Say I have a class Customerwhich has a property FirstName. Then I have a List<Customer>.
假设我有一个Customer具有属性的类FirstName。然后我有一个List<Customer>.
Can LINQ be used to find if the list has a customer with Firstname = 'John'in a single statement.. how?
可以使用 LINQ 来查找列表中是否有一个客户Firstname = 'John'在单个语句中......如何？
采纳答案by zvolkov
LINQ defines an extension method that is perfect for solving this exact problem:
LINQ 定义了一个非常适合解决这个确切问题的扩展方法：
using System.Linq;
...
bool has = list.Any(cus => cus.FirstName == "John");
make sure you reference System.Core.dll, that's where LINQ lives.
确保您引用了 System.Core.dll，这就是 LINQ 所在的位置。
回答by Chris Brandsma
customerList.Any(x=>x.Firstname == "John")
回答by M4N
List<Customer> list = ...;
Customer john = list.SingleOrDefault(customer => customer.Firstname == "John");
john will be null if no customer exists with a first name of "John".
如果不存在名字为“John”的客户，则 john 将为 null。
回答by Jon Skeet
zvolkov's answer is the perfect one to find out ifthere is such a customer. If you need to usethe customer afterwards, you can do:
zvolkov 的回答是找出是否有这样一位客户的完美答案。如果您事后需要使用客户，您可以这样做：
Customer customer = list.FirstOrDefault(cus => cus.FirstName == "John");
if (customer != null)
{
// Use customer
}
I know this isn't what you were asking, but I thought I'd pre-empt a follow-on question :) (Of course, this only finds the firstsuch customer... to find all of them, just use a normal whereclause.)
我知道这不是你要问的，但我想我会先发制人的后续问题:)（当然，这只会找到第一个这样的客户......要找到所有这些客户，只需使用正常where条款。）
回答by Krassi
Another possibility
另一种可能
if (list.Count(customer => customer.Firstname == "John") > 0) {
//bla
}
回答by jmservera
Using Linq you have many possibilities, here one without using lambdas:
使用 Linq 你有很多可能性，这里有一个不使用 lambdas：
//assuming list is a List<Customer> or something queryable...
var hasJohn = (from customer in list
where customer.FirstName == "John"
select customer).Any();
回答by Mike Sackton
One option for the follow on question (how to find a customer who might have any number of first names):
以下问题的一个选项（如何查找可能有任意数量名字的客户）：
List<string> names = new List<string>{ "John", "Max", "Pete" };
bool has = customers.Any(cus => names.Contains(cus.FirstName));
or to retrieve the customer from csv of similar list
或从类似列表的 csv 中检索客户
string input = "John,Max,Pete";
List<string> names = input.Split(',').ToList();
customer = customers.FirstOrDefault(cus => names.Contains(cus.FirstName));
回答by Ian Boyd
The technique i used before discovering .Any():
我在发现之前使用的技术.Any()：
var hasJohn = (from customer in list
where customer.FirstName == "John"
select customer).FirstOrDefault() != null;
回答by Fabio Stratotti
Try this, I hope it helps you.
试试这个，希望对你有帮助。
if (lstCustumers.Any(cus => cus.Firstname == "John"))
{
//TODO CODE
}
