C# Linq - SET syntax from SQL, i.e. SET abc (a property of obj) WHERE xyz = true in IEnumerable<obj>

Question

I have a collection of Obj's, I want to go through the collection, and set a property if a condition is true, so in normal world it would be:

foreach (var o in obj)
{
   if (o.SomeProperty == Something)
   {
      o.SomeOtherProperty = true;
   }
}

Anyway to do this, using Linq, to make it in a single line?

Answer 1

LINQ isn't all that useful for executing side effects, it's primarily intended for querying. In truth, the fact that it has deferred execution so engrained in its behaviour makes it a poor choice for executing side-effects, IMO.

The code you've got looks perfectly fine to me. If you did want to use LINQ though, I doubt you could improve much on:

foreach (var o in obj.Where(i => i.SomeProperty == Something))
{
   o.SomeOtherProperty = true;
}  

Now, that isn't all that better (arguably worse) than your original.

On the other hand, if you wanted to create a new, streaming sequence with projections of the original items having the desired characteristics, you could do something like:

var projection = obj.Where(i => i.SomeProperty == Something)
                    .Select(i => new Foo(i) { SomeOtherProperty = true });
                    // assuming your type has a copy-constructor

EDIT: If you don't want to heed the advice of the experts (read: Eric Lippert), you can write your own extension-method:

public static void Do<T>(this IEnumerable<T> source, Action<T> action)
{ 
  if (source == null)
     throw new ArgumentNullException("source");

  if (action == null)
     throw new ArgumentNullException("action");

  foreach (T item in source) 
     action(item);
}

This will allow you to do:

obj.Where(o => o.SomeProperty == Something)
   .Do(o => o.SomeOtherProperty = true);

Answer 2

obj.Where(i => i.SomeProperty == Something).ToList().ForEach(o => o.SomeOtherProperty = true);  

Answer 3

You could do this:

myCollection.ForEach(item => 
    if(item.SomeProperty==Something){item.SomeOtherProperty = true});

But I wouldn't recommend it; you're not really saving much at all, and it loses a little bit of readability, IMO.

Answer 4

Using an extension method:

public static int UpdateOnPredication<T>(this IEnumerable<T> source, Func<T, bool> predicate, Action<T> update)
{
    //check the parameters here if (source==null) ...
    var query = source.Where(predicate);
    foreach (var item in query)
    {
        update(item);
    }
    return query.Count();
}

Usage:

results.UpdateOnPredication(x => x.ID > 1000, x => x.Status = 1);