如何处理从 lambda 选择返回的空值？

Question

I am using the following lambda selection

if (users.Any(x => x.userId.ToString() == id))
{
     var user = _users.First(x => x.userId.ToString() == id);
    _users.Remove(user);
}
//use entitybase to setup the user and its id.i have left that bit out 
_users.Add(user)

There are no values in the users list that match id so the line

users.Any(x => x.userId.ToString() == id  // gives a "Object reference exception"

Is there a selection in lambda i can use that takes care of nulls.

Answer 1

I'd suggest to instead of .ToString() , parse id to the type userId is.

Then:

// this is compeletely unneccessary
//if (users.Any(x => x.userId.ToString() == id))
//{
     // vv this assumes that if x is not null, property `userId` is required, so cannot be null
     var user = _users.FirstOrDefault(x => !(x is null) && x.userId == id);
     if(!(user is null)) // C# 9 : if( user is not null )
     {
         _users.Remove(user);
     }
//}

Alternative Linq:

var user = _users.Where(x => !(x is null)).FirstOrDefault(x => x.userId ==id);

Not sure which one would perform better. I'd probably benchmark this.