Queryable.First(Of TSource) Method (IQueryable(Of TSource))
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Returns the first element of a sequence.
Assembly: System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared Function First(Of TSource) ( _ source As IQueryable(Of TSource) _ ) As TSource
Type Parameters
- TSource
The type of the elements of source.
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.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable(Of TSource). When you use instance method syntax to call this method, omit the first parameter.| Exception | Condition |
|---|---|
| ArgumentNullException | source is Nothing. |
| 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.