Enumerable.DefaultIfEmpty<'TSource> Method (IEnumerable<'TSource>)
Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty.
Assembly: System.Core (in System.Core.dll)
static member DefaultIfEmpty<'TSource> : source:IEnumerable<'TSource> -> IEnumerable<'TSource>
The sequence to return a default value for if it is empty.
Return ValueType: System.Collections.Generic.IEnumerable<'TSource>
An IEnumerable<'T> object that contains the default value for the TSource type if source is empty; otherwise, source.
The type of the elements of source.
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
The default value for reference and nullable types is null.
This method can be used to produce a left outer join when it is combined with the GroupJoin<'TOuter, 'TInner, 'TKey, 'TResult>) method.
The following code examples demonstrate how to useto provide a default value in case the source sequence is empty.
This example uses a non-empty sequence.
This example uses an empty sequence.
Available since 8
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Available since 8.1