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Queryable.Concat<TSource> Method

Concatenates two sequences.

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

public static IQueryable<TSource> Concat<TSource>(
	this IQueryable<TSource> source1,
	IEnumerable<TSource> source2

Type Parameters


The type of the elements of the input sequences.


Type: System.Linq.IQueryable<TSource>
The first sequence to concatenate.
Type: System.Collections.Generic.IEnumerable<TSource>
The sequence to concatenate to the first sequence.

Return Value

Type: System.Linq.IQueryable<TSource>
An IQueryable<T> that contains the concatenated elements of the two input sequences.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


source1 or source2 is null.

The Concat<TSource>(IQueryable<TSource>, IEnumerable<TSource>) method generates a MethodCallExpression that represents calling Concat<TSource>(IQueryable<TSource>, IEnumerable<TSource>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source1 parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Concat<TSource>(IQueryable<TSource>, IEnumerable<TSource>) depends on the implementation of the type of the source1 parameter. The expected behavior is that the elements in source2 are concatenated to those of source1 to create a new sequence.

The following code example demonstrates how to use Concat<TSource>(IQueryable<TSource>, IEnumerable<TSource>) to concatenate two sequences.

            class Pet
                public string Name { get; set; }
                public int Age { get; set; }

            // This method creates and returns an array of Pet objects.
            static Pet[] GetCats()
                Pet[] cats = { new Pet { Name="Barley", Age=8 },
                               new Pet { Name="Boots", Age=4 },
                               new Pet { Name="Whiskers", Age=1 } };
                return cats;

            // This method creates and returns an array of Pet objects.
            static Pet[] GetDogs()
                Pet[] dogs = { new Pet { Name="Bounder", Age=3 },
                               new Pet { Name="Snoopy", Age=14 },
                               new Pet { Name="Fido", Age=9 } };
                return dogs;

            public static void ConcatEx1()
                Pet[] cats = GetCats();
                Pet[] dogs = GetDogs();

                // Concatenate a collection of cat names to a
                // collection of dog names by using Concat().
                IEnumerable<string> query =
                    .Select(cat => cat.Name)
                    .Concat(dogs.Select(dog => dog.Name));

                foreach (string name in query)

            // This code produces the following output:
            // Barley
            // Boots
            // Whiskers
            // Bounder
            // Snoopy
            // Fido

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.