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.
Assembly: System.Core (in System.Core.dll)
static member DefaultIfEmpty<'TSource> : source:IQueryable<'TSource> -> IQueryable<'TSource>
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).
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