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{TOC}

Back to Standard Query Operator Index


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Introduction

The Single operator returns the single element of a sequence.

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Method Signatures

// 1 - Get the first and only record
public static TSource Single<TSource>(
    this IEnumerable<TSource> source)
 
// 2 - Gets the only record that passes the predicate function
public static TSource Single<TSource>(
    this IEnumerable<TSource> source, 
    Func<TSource, bool> predicate)

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Exceptions

Throws an ArgumentNullException if source or predicate is null.
Throws an InvalidOperationException if source is empty.
Throws an InvalidOperationException if no records, or more than one record pass the predicate function.


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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, throw an InvalidOperationException.
If counter > 1 (more than one element passed the predicate function), throw an InvalidOperationException.
Return the one and only element that passed the predicate.


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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.


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Code Samples

TODO: Needs code sample.