How to add an item in a collection using Linq and C#

Question

I have a collection of objects. e.g.

List<Subscription> subscription = new List<Subscription>
{
    new Subscription{ Type = "Trial", Type = "Offline", Period = 30  },
    new Subscription{ Type = "Free",  Type = "Offline", Period = 90  },
    new Subscription{ Type = "Paid",  Type = "Online",  Period = 365 }
};

Now I want to add one more item in this list using LINQ. How can I do this?

Solution 1

You don't. LINQ is for querying, not adding. You add a new item by writing:

subscription.Add(new Subscription { Type = "Foo", Type2 = "Bar", Period = 1 });

(Note that you can't specify the property Type twice in the same object initializer.)

This isn't using LINQ at all - it's using object initializers and the simple List<T>.Add method.

Solution 2

I would suggest using List.Add():

subscription.Add(new Subscriptioin(...))

LINQ Union() overkill by wrapping a single item by a List<> instance:

subscriptions.Union(new List<Subscription> { new Subscriptioin(...) };

Comments

[Sedat Kapanoglu]

To elaborate on the second approach, it's the functional approach which treats modified versions of lists as new instances. This allows list immutability and has certain inherent advantages in functional programming model. It may not be as performant though depending on the scenario. For further reference: en.wikipedia.org/wiki/Immutable_object

[Maxim Gershkovich]

There are kinda exceptions to this. For example needing to append an empty ListItem to a collection for the purposes of display. In this scenario you can accomplish this with a Union as such StockCollection.Union(new[] { new Stock() { Name = "" } }). While this is certainly not a great practice sometimes its useful.

[Maxim Gershkovich]

I've used it like this in MVC @Html.DropDownListFor(o => o.StockID, Model.Stock.Union(new[] { new Stock() { Name = "" } }).Select(o => new SelectListItem() { Text = o.Name, Value = o.StockID.ToString() })

[Jon Skeet]

@MaximGershkovich: That isn't appending a list item to a collection. It's creating a new sequence out of two sequences. (Personally I'd use Concat rather than Union, but that's a different matter.) "Adding an item to a collection" necessarily changes the contents of the collection - you're not doing that.

[Maxim Gershkovich]

Fair enough but I feel like that's arguing about semantics rather than the actual intent of the OP.

[Jon Skeet]

@Maxim: the intent of the OP seems to be adding to a collection, given that that's what was asked for. Union simply doesn't do that.