<ExtensionAttribute()>
Public Overloads Shared Function LongCount(Of TSource)( _
   ByVal source As IEntityScalarQuery(Of TSource), _
   Optional ByVal userCallback As Action(Of EntityScalarQueryOperation(Of Long)), _
   Optional ByVal userState As Object _
) As EntityScalarQueryOperation(Of Long)

Dim source As IEntityScalarQuery(Of TSource)
Dim userCallback As Action(Of EntityScalarQueryOperation(Of Long))
Dim userState As Object
Dim value As EntityScalarQueryOperation(Of Long)
 
value = EntityScalarAsyncExtensions.LongCount(Of TSource)(source, userCallback, userState)

[ExtensionAttribute()]
public static EntityScalarQueryOperation<long> LongCount<TSource>( 
   IEntityScalarQuery<TSource> source,
   Action<EntityScalarQueryOperation<long>> userCallback,
   object userState
)

[ExtensionAttribute()]
public:
static EntityScalarQueryOperation<int64>^ LongCountgeneric<typename TSource>
( 
   IEntityScalarQuery<TSource^>^ source,
   Action<EntityScalarQueryOperation<int64>^>^ userCallback,
   Object^ userState
) 

public void AsyncLongCount() {
  var op = _entityManager.OrderSummaries.AsScalarAsync().LongCount();
  op.Completed += (o, e) => {
    var ct = e.Result;
  };
}