Is it possible to use List <T> .Contains (...)?

Question

I am trying to create a general cache class that will contain a list of objects
, and will expose a method that allows you to check whether the object instance has already been cached based on the Id property:

public class CacheService<T> where T : BaseModel { private List<T> _data = new List<T>(); public void Check(T obj) { if (_data.Contains(r => r.Id.Equals(obj.Id)) { //Do something } } } public class BaseModel { public int Id { get; set; } } 

I get a compiler error in the Contains() command saying:

Cannot convert lambda expression to type 'T' because it is not a delegate type

How can I achieve my goal?

Answer 1

You can use Linq:

 bool contains = _data.Any(r => r.Id.Equals(obj.Id)); 

or List.Exists :

 bool contains = _data.Exists(r => r.Id.Equals(obj.Id)); 

Answer 2

Use the LINQ Any function instead of Contains . For List<T> the Contains method is defined as a T