Enumerable::DefaultIfEmpty<TSource> Method (IEnumerable<TSource>^, TSource)

 

Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

public:
generic<typename TSource>
[ExtensionAttribute]
static IEnumerable<TSource>^ DefaultIfEmpty(
	IEnumerable<TSource>^ source,
	TSource defaultValue
)

Parameters

source
Type: System.Collections.Generic::IEnumerable<TSource>^

The sequence to return the specified value for if it is empty.

defaultValue
Type: TSource

The value to return if the sequence is empty.

Return Value

Type: System.Collections.Generic::IEnumerable<TSource>^

An IEnumerable<T> that contains defaultValue if source is empty; otherwise, source.

Type Parameters

TSource

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.

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 example demonstrates how to use the DefaultIfEmpty<TSource>(IEnumerable<TSource>^, TSource) method and specify a default value. The first sequence is not empty and the second sequence is empty.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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