QueryableExtensions.FirstOrDefaultAsync<TSource> Method (IQueryable<TSource>, CancellationToken)

Article
12/10/2014

[This page is specific to the Entity Framework version 6. The latest version is available as the 'Entity Framework' NuGet package. For more information about Entity Framework, see msdn.com/data/ef.]

Asynchronously returns the first element of a sequence, or a default value if the sequence contains no elements.

Namespace: System.Data.Entity
Assembly: EntityFramework (in EntityFramework.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function FirstOrDefaultAsync(Of TSource) ( _
    source As IQueryable(Of TSource), _
    cancellationToken As CancellationToken _
) As Task(Of TSource)
'Usage
Dim source As IQueryable(Of TSource)
Dim cancellationToken As CancellationToken 
Dim returnValue As Task(Of TSource)

returnValue = source.FirstOrDefaultAsync(cancellationToken)

public static Task<TSource> FirstOrDefaultAsync<TSource>(
    this IQueryable<TSource> source,
    CancellationToken cancellationToken
)

[ExtensionAttribute]
public:
generic<typename TSource>
static Task<TSource>^ FirstOrDefaultAsync(
    IQueryable<TSource>^ source, 
    CancellationToken cancellationToken
)

static member FirstOrDefaultAsync : 
        source:IQueryable<'TSource> * 
        cancellationToken:CancellationToken -> Task<'TSource>

JScript does not support generic types and methods.

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
An IQueryable<T> to return the first element of.

cancellationToken
Type: System.Threading.CancellationToken
A CancellationToken to observe while waiting for the task to complete.

Return Value

Type: System.Threading.Tasks.Task<TSource>
A task that represents the asynchronous operation. The task result contains default ( TSource ) if source is empty; otherwise, the first element in source.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see https://msdn.microsoft.com/en-us/library/bb384936(v=vs.113) or https://msdn.microsoft.com/en-us/library/bb383977(v=vs.113).

Exceptions

Exception	Condition
ArgumentNullException	source is null .
InvalidOperationException	source does not implement IDbAsyncQueryProvider .

Remarks

Multiple active operations on the same context instance are not supported. Use 'await' to ensure that any asynchronous operations have completed before calling another method on this context.