ParallelEnumerable.Union<TSource> Method (ParallelQuery<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>)

Note: This API is now obsolete.

This Union overload should never be called. This method is marked as obsolete and always throws NotSupportedException when called.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

[ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
public static ParallelQuery<TSource> Union<TSource>(
	this ParallelQuery<TSource> first,
	IEnumerable<TSource> second,
	IEqualityComparer<TSource> comparer


Type: System.Linq.ParallelQuery<TSource>

This parameter is not used.

Type: System.Collections.Generic.IEnumerable<TSource>

This parameter is not used.

Type: System.Collections.Generic.IEqualityComparer<TSource>

This parameter is not used.

Return Value

Type: System.Linq.ParallelQuery<TSource>

This overload always throws a NotSupportedException.

Type Parameters


This type parameter is not used.

Exception Condition

The exception that occurs when this method is called.


The query was canceled with the token passed in through WithCancellation.


One or more exceptions occurred during the evaluation of the query.

This overload exists to disallow usage of Union with a left data source of type ParallelQuery<TSource> and a right data source of type IEnumerable<T>. Otherwise, the Union operator would appear to be binding to the parallel implementation, but would in reality bind to the sequential implementation.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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