Queryable.First(Of TSource) Method (IQueryable(Of TSource))
Returns the first element of a sequence.
Assembly: System.Core (in System.Core.dll)
<ExtensionAttribute> Public Shared Function First(Of TSource) ( source As IQueryable(Of TSource) ) As TSource
Parameters
- source
-
Type:
System.Linq.IQueryable(Of TSource)
The IQueryable(Of T) to return the first element of.
Return Value
Type: TSourceThe first element in source.
Type Parameters
- TSource
The type of the elements of source.
| Exception | Condition |
|---|---|
| ArgumentNullException | source is null. |
| InvalidOperationException | The source sequence is empty. |
The First(Of TSource)(IQueryable(Of TSource)) method generates a MethodCallExpression that represents calling First(Of TSource)(IQueryable(Of TSource)) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute(Of 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 First(Of TSource)(IQueryable(Of TSource)) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the first element in source.
The following code example demonstrates how to use First(Of TSource)(IQueryable(Of TSource)) to return the first element in a sequence.
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