QueryableExtensions.FirstOrDefaultAsync<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, Boolean>>)

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 that satisfies a specified condition or a default value if no such element is found.

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

Syntax

'Declaration
<SuppressMessageAttribute("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")> _
<ExtensionAttribute> _
Public Shared Function FirstOrDefaultAsync(Of TSource) ( _
    source As IQueryable(Of TSource), _
    predicate As Expression(Of Func(Of TSource, Boolean)) _
) As Task(Of TSource)
'Usage
Dim source As IQueryable(Of TSource)
Dim predicate As Expression(Of Func(Of TSource, Boolean))
Dim returnValue As Task(Of TSource)

returnValue = source.FirstOrDefaultAsync(predicate)

[SuppressMessageAttribute("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")]
public static Task<TSource> FirstOrDefaultAsync<TSource>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, bool>> predicate
)

[SuppressMessageAttribute(L"Microsoft.Design", L"CA1006:DoNotNestGenericTypesInMemberSignatures")]
[ExtensionAttribute]
public:
generic<typename TSource>
static Task<TSource>^ FirstOrDefaultAsync(
    IQueryable<TSource>^ source, 
    Expression<Func<TSource, bool>^>^ predicate
)

[<SuppressMessageAttribute("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")>]
static member FirstOrDefaultAsync : 
        source:IQueryable<'TSource> * 
        predicate:Expression<Func<'TSource, bool>> -> 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.

predicate
Type: System.Linq.Expressions.Expression<Func<TSource, Boolean>>
A function to test each element for a condition.

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 or if no element passes the test specified by predicate ; otherwise, the first element in source that passes the test specified by predicate.

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 or predicate 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.

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