<ExtensionAttribute()>
Public Overloads Shared Function Sum( _
   ByVal source As IEntityScalarQuery, _
   ByVal projectionSelector As IProjectionSelector, _
   Optional ByVal userCallback As Action(Of EntityScalarQueryOperation), _
   Optional ByVal userState As Object _
) As EntityScalarQueryOperation

Dim source As IEntityScalarQuery
Dim projectionSelector As IProjectionSelector
Dim userCallback As Action(Of EntityScalarQueryOperation)
Dim userState As Object
Dim value As EntityScalarQueryOperation
 
value = EntityScalarAsyncExtensions.Sum(source, projectionSelector, userCallback, userState)

[ExtensionAttribute()]
public static EntityScalarQueryOperation Sum( 
   IEntityScalarQuery source,
   IProjectionSelector projectionSelector,
   Action<EntityScalarQueryOperation> userCallback,
   object userState
)

[ExtensionAttribute()]
public:
static EntityScalarQueryOperation^ Sum( 
   IEntityScalarQuery^ source,
   IProjectionSelector^ projectionSelector,
   Action<EntityScalarQueryOperation^>^ userCallback,
   Object^ userState
) 

public void AsyncSumWithPredicate() {
  var op = _entityManager.OrderSummaries.AsScalarAsync().Sum<OrderSummary, Nullable<Decimal>>(o => o.Freight);
  op.Completed += (o, e) => {
    var ct = e.Result;
  };
}