DefaultIfEmpty(TSource) Method (IQueryable(TSource))
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Queryable::DefaultIfEmpty<TSource> Method (IQueryable<TSource>^)

 

Returns the elements of the specified sequence or the type parameter's default 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 IQueryable<TSource>^ DefaultIfEmpty(
	IQueryable<TSource>^ source
)

Parameters

source
Type: System.Linq::IQueryable<TSource>^

The IQueryable<T> to return a default value for if empty.

Return Value

Type: System.Linq::IQueryable<TSource>^

An IQueryable<T> that contains default(TSource) if source is empty; otherwise, source.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source is null.

The DefaultIfEmpty<TSource>(IQueryable<TSource>^) method generates a MethodCallExpression that represents calling DefaultIfEmpty<TSource>(IQueryable<TSource>^) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression^) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling DefaultIfEmpty<TSource>(IQueryable<TSource>^) depends on the implementation of the type of the source parameter. The expected behavior is that it returns source if it is not empty. Otherwise, it returns an IQueryable<T> that contains default(TSource).

The following code examples demonstrate how to use DefaultIfEmpty<TSource>(IQueryable<TSource>^) to provide a default value in case the source 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 7.1
Windows Phone
Available since 8.1
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