Enumerable.DefaultIfEmpty(TSource) Method (IEnumerable(TSource), TSource)
Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable(TSource)
The sequence to return the specified value for if it is empty.
- defaultValue
- Type: TSource
The value to return if the sequence is empty.
Return Value
Type: System.Collections.Generic.IEnumerable(TSource)An IEnumerable(T) that contains defaultValue if source is empty; otherwise, source.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(TSource). When you use instance method syntax to call this method, omit the first parameter.This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
This method can be used to produce a left outer join when it is combined with the GroupJoin) method.
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