Queryable.Single(TSource) Method (IQueryable(TSource))

Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.

Namespace:  System.Linq
Assemblies:   System.Linq.Queryable (in System.Linq.Queryable.dll)
  System.Core (in System.Core.dll)

static member Single : 
        source:IQueryable<'TSource> -> 'TSource 

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable(TSource)

An IQueryable(T) to return the single element of.

Return Value

Type: TSource
The single element of the input sequence.

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 Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source is a null reference (Nothing in Visual Basic).

InvalidOperationException

source has more than one element.

The Single(TSource)(IQueryable(TSource)) method generates a MethodCallExpression that represents calling Single(TSource)(IQueryable(TSource)) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute(TResult)(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 Single(TSource)(IQueryable(TSource)) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the only element in source.

The following code example demonstrates how to use Single(TSource)(IQueryable(TSource)) to select the only element of an array.

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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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