Queryable.ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) Method

Definition

Namespace:: System.Linq

Assembly:: System.Linq.Queryable.dll

Assembly:: System.Core.dll

Assembly:: netstandard.dll

Returns the element at a specified index in a sequence or a default value if the index is out of range.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static TSource ElementAtOrDefault(System::Linq::IQueryable<TSource> ^ source, int index);

public static TSource ElementAtOrDefault<TSource> (this System.Linq.IQueryable<TSource> source, int index);

public static TSource ElementAtOrDefault<TSource> (this System.Linq.IQueryable<TSource>? source, int index);

static member ElementAtOrDefault : System.Linq.IQueryable<'Source> * int -> 'Source

<Extension()>
Public Function ElementAtOrDefault(Of TSource) (source As IQueryable(Of TSource), index As Integer) As TSource

Type Parameters

TSource

The type of the elements of source.

Parameters

source: IQueryable<TSource>

An IQueryable<T> to return an element from.

index: Int32

The zero-based index of the element to retrieve.

Returns

TSource

default(TSource) if index is outside the bounds of source; otherwise, the element at the specified position in source.

Exceptions

ArgumentNullException

source is null.

Examples

The following code example demonstrates how to use ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32). This example uses a value for index that is outside the bounds of the source sequence.

string[] names = { "Hartono, Tommy", "Adams, Terry",
                   "Andersen, Henriette Thaulow",
                   "Hedlund, Magnus", "Ito, Shu" };

int index = 20;

string name = names.AsQueryable().ElementAtOrDefault(index);

Console.WriteLine(
    "The name chosen at index {0} is '{1}'.",
    index,
    String.IsNullOrEmpty(name) ? "[NONE AT THIS INDEX]" : name);

/*
    This code produces the following output:

    The name chosen at index 20 is '[NONE AT THIS INDEX]'.
*/

Dim names() As String = {"Hartono, Tommy", "Adams, Terry", _
                   "Andersen, Henriette Thaulow", _
                   "Hedlund, Magnus", "Ito, Shu"}

Dim index As Integer = 20

Dim name As String = names.AsQueryable().ElementAtOrDefault(index)

MsgBox(String.Format("The name at index {0} is '{1}'.", _
    index, IIf(String.IsNullOrEmpty(name), "[NONE AT THIS INDEX]", name)))

' This code produces the following output:
'
' The name at index 20 is '[NONE AT THIS INDEX]'.

Remarks

The ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) method generates a MethodCallExpression that represents calling ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) 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 ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the item at position index in source, or default(TSource) if index is outside the bounds of source.

Applies to