Navigation

• Home Page
• Advanced Search
• Categories
• All Pages (136)
• Recent Changes
• Resource links
• LINQ Books

5 Minute Overviews

• LINQ to Objects
• LINQ to SQL
• LINQ to XML

FAQ (new)

• LINQ to Objects
• LINQ to SQL
• LINQ to XML

Content

• Login/Logout
• Language Selection
• Your Profile
• Create Account

• Create a new Page
• File Management
• Editing Help
• Practise Editing
• About this Site
• Contact me

• Administration

{TOC}

Back to Standard Query Operator Index


Edit

Introduction

The SingleOrDefault operator returns the single element of a sequence, or a default value if no element is found.

Edit

Method Signatures

// 1 - Return the first and only element.
// If there is no elements or more than one, return default(TSource).
public static TSource SingleOrDefault<TSource>(
    this IEnumerable<TSource> source)
 
// 2 - Return the first and only element that passed the predicate function.
// If there is no elements or more than one, return default(TSource).
public static TSource SingleOrDefault<TSource>(
    this IEnumerable<TSource> source, 
    Func<TSource, bool> predicate)
 

Edit

Exceptions

Throws an ArgumentNullException if source or predicate is null.

Edit

Pseudo-code

Overload 1
If source is null, throw an ArgumentNullException.
If source is of type IList.
Else
Overload 2
If source is null, throw an ArgumentNullException.
If predicate is null, throw an ArgumentNullException.
Initialize a counter to zero.
Iterate the source sequence.
If counter is zero, return default(TSource);.
If counter > 1 (more than one element passed the predicate function), return default(TSource);.
Return the one and only element that passed the predicate.


Edit

Loop Count

Overload 1
< 1. If source is an IList type, the first element is accessed by index which is very quick, otherwise the first (and second if it exists) is enumerated.


Overload 2
1. Source is iterated once to find a matching element or to ascertain if there is more than one element that passes the predicate function.


Edit

Code Samples

int[] ageMaster = { 11, 21, 31, 41, 51 };

try { ageMaster.Single (n => n > 60); } catch (Exception ex) { ex.Message.Dump ("The Single age > 60"); }

ageMaster.SingleOrDefault (n => n > 50).Dump ("The SingleOrDefault age > 50");

ageMaster.SingleOrDefault (n => n < 10).Dump("The SingleOrDefault age < 10");