<ExtensionAttribute()>
Public Overloads Shared Function SelectMany
    (Of TSource,TResult)( _
   ByVal source As IEntityQuery(Of TSource), _
   ByVal selector As Expression(Of Func(Of TSource,IEnumerable(Of TResult))) _
) As IEntityQuery(Of TResult)

Dim source As IEntityQuery(Of TSource)
Dim selector As Expression(Of Func(Of TSource,IEnumerable(Of TResult)))
Dim value As IEntityQuery(Of TResult)
 
value = EntityQueryExtensions.SelectMany(Of TSource, TResult)(source, selector)

[ExtensionAttribute()]
public static IEntityQuery<TResult> SelectMany<TSource,TResult>( 
   IEntityQuery<TSource> source,
   Expression<Func<TSource,IEnumerable<TResult>>> selector
)

[ExtensionAttribute()]
public:
static IEntityQuery<TResult^>^ SelectManygeneric<typename TSource>
generic<typename TResult>
( 
   IEntityQuery<TSource^>^ source,
   Expression<Func<TSource^,IEnumerable<TResult^>^>^>^ selector
) 

var mgr = new DomainModelEntityManager();

var baseQuery = mgr.Customers;
var query = baseQuery.Take(2).SelectMany(c => c.OrderSummaries);
var results = query.Execute();