tags

linq

Using foreach with index in C#

Just a quick tip today! for and foreach loops are among the most useful constructs in a C# developer's toolbox. To iterate a collection, foreach is, in my opinion, more convenient than for in most cases. It works with all collection types, including those that are not indexable such as IEnumerable<T>, and doesn't require to access the current element by its index. But sometimes, you do need the index of the current item; this usually leads to one of these patterns:

Linq performance improvements in .NET Core

By now, you're probably aware that Microsoft released an open-source and cross-platform version of the .NET platform: .NET Core. This means you can now build and run .NET apps on Linux or macOS. This is pretty cool in itself, but it doesn't end there: .NET Core also brings a lot of improvements to the Base Class Library. For instance, Linq has been made faster in .NET Core. I made a little benchmark to compare the performance of some common Linq methods, and the results are quite impressive:

Optimize ToArray and ToList by providing the number of elements

The ToArray and ToList extension methods are convenient ways to eagerly materialize an enumerable sequence (e.g. a Linq query) into an array or a list. However, there’s something that bothers me: both of these methods are very inefficient if they don’t know the number of elements in the sequence (which is almost always the case when you use them on a Linq query). Let’s focus on ToArray for now (ToList has a few differences, but the principle is mostly the same).

[WPF] Using Linq to shape data in a CollectionView

WPF provides a simple mechanism for shaping collections of data, via the ICollectionView interface and its Filter, SortDescriptions and GroupDescriptions properties: // Collection to which the view is bound public ObservableCollection People { get; private set; } ... // Default view of the People collection ICollectionView view = CollectionViewSource.GetDefaultView(People); // Show only adults view.Filter = o => ((Person)o).Age >= 18; // Sort by last name and first name view.SortDescriptions.Add(new SortDescription("LastName", ListSortDirection.

[Entity Framework] Using Include with lambda expressions

I'm currently working on a project that uses Entity Framework 4. Even though lazy loading is enabled, I often use the ObjectQuery.Include method to eagerly load associated entities, in order to avoid database roundtrips when I access them: var query = from ord in db.Orders.Include("OrderDetails") where ord.Date >= DateTime.Today select ord; Or if I also want to eagerly load the product: var query = from ord in db.Orders.Include("OrderDetails.Product") where ord.Date >= DateTime.

Automating null checks with Linq expressions

The problem Have you ever written code like the following ? X xx = GetX(); string name = "Default"; if (xx != null && xx.Foo != null && xx.Foo.Bar != null && xx.Foo.Bar.Baz != null) { name = xx.Foo.Bar.Baz.Name; } I bet you have ! You just need to get the value of xx.Foo.Bar.Baz.Name, but you have to test every intermediate object to ensure that it's not null. It can quickly become annoying if the property you need is nested in a deep object graph….