Sum(TSource) Method (IQueryable(TSource), Expression(Func(TSource, Nullable(Int64))))

Queryable.Sum(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Int64))))

 

Computes the sum of the sequence of nullable Int64 values that is obtained by invoking a projection function on each element of the input sequence.

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

<ExtensionAttribute>
Public Shared Function Sum(Of TSource) (
	source As IQueryable(Of TSource),
	selector As Expression(Of Func(Of TSource, Nullable(Of Long)))
) As Nullable(Of Long)

Parameters

source
Type: System.Linq.IQueryable(Of TSource)

A sequence of values of type TSource.

selector
Type: System.Linq.Expressions.Expression(Of Func(Of TSource, Nullable(Of Int64)))

A projection function to apply to each element.

Return Value

Type: System.Nullable(Of Int64)

The sum of the projected values.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source or selector is null.

OverflowException

The sum is larger than MaxValue.

This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).

The Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Int64)))) method generates a MethodCallExpression that represents calling Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Int64)))) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute(Of TResult)(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Int64)))) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source and returns the sum of the resulting values.

The following code example demonstrates how to use Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Double))) to sum the projected values of a sequence.

System_CAPS_noteNote

This code example uses an overload of this overloaded method that is different from the specific overload that this topic describes. To extend the example to this topic, change the body of the selector function.

Structure Package
    Public Company As String
    Public Weight As Double
End Structure

Shared Sub SumEx3()
    Dim packages As New List(Of Package)(New Package() { _
            New Package With {.Company = "Coho Vineyard", .Weight = 25.2}, _
              New Package With {.Company = "Lucerne Publishing", .Weight = 18.7}, _
              New Package With {.Company = "Wingtip Toys", .Weight = 6.0}, _
              New Package With {.Company = "Adventure Works", .Weight = 33.8}})

    ' Calculate the sum of all package weights.
    Dim totalWeight As Double = packages.AsQueryable().Sum(Function(pkg) pkg.Weight)

    MsgBox("The total weight of the packages is: " & totalWeight)
End Sub

'This code produces the following output:

'The total weight of the packages is: 83.7

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
Return to top
Show:
© 2016 Microsoft