Linq to Objects to query LLBLGen projection

Question

I'm trying to use the recommended LLBLGen syntax to query a projection (http://www.llblgen.com/documentation/3.5/LLBLGen%20Pro%20RTF/Using%20the%20generated%20code/Adapter/gencode_usingentityview_adapter.htm#projections)

IEntityView2 view = table.DefaultView;
List<A1AllocationHelp1TableDTO> something = 
    (from c in view
     select new A1AllocationHelp1TableDTO
     {
         RecordStatus = c.RecordStatus,
         UniqueIdent = c.UniqueIdent
     }).ToList();

But I'm getting this error on 'select':

The type arguments for method 'IEnumerable<TResult>
System.Linq.Enumerable.Select<TSource, TResult>(this IEnumerable<TSource>,
Func<TSource, TResult>)' cannot be inferred from the query.

Funny is that the same works just fine in VB.Net

Dim view As IEntityView2 = table.DefaultView
Dim something As List(Of A1AllocationHelp1TableDTO) = _
    (From c In view
     Select New A1AllocationHelp1TableDTO With _
          {
              .RecordStatus = c.RecordStatus, _
              .UniqueIdent = c.UniqueIdent
          }).ToList()

I'm using VS2010, .NET 4 and LLBLGen 2.6. Can't figure out how to fix this can anyone give me a hand?

Thanks

Edit:

IEntityView2 is generated by LLBLGen and this is its definition

public interface IEntityView2 : IEnumerable
{
    bool AllowEdit { get; set; }
    bool AllowNew { get; set; }
    bool AllowRemove { get; set; }
    int Count { get; }
    PostCollectionChangeAction DataChangeAction { get; set; }
    IPredicate Filter { get; set; }
    IEntityCollection2 RelatedCollection { get; }
    ISortExpression Sorter { get; set; }
    IEntity2 this[int index] { get; }
    event ListChangedEventHandler ListChanged;
    bool Contains(IEntity2 value);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, DataTable destination);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityCollection2 destination);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityDataProjector projector);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, DataTable destination, bool allowDuplicates);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityCollection2 destination, bool allowDuplicates);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityDataProjector projector, bool allowDuplicates);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, DataTable destination, bool allowDuplicates, IPredicate filter);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityCollection2 destination, bool allowDuplicates, IPredicate filter);
    void CreateProjection(List<IEntityPropertyProjector> propertyProjectors, IEntityDataProjector projector, bool allowDuplicates, IPredicate filter);
    int IndexOf(IEntity2 value);
    IEntityCollection2 ToEntityCollection();
    IEntityCollection2 ToEntityCollection(int startIndex);
}

Please show the definition of `IEntityView2`. – Daniel Hilgarth Mar 21 '13 at 08:28 — Daniel Hilgarth, Mar 21 '13 at 08:28
I've edited to add the definition – kooshka Mar 21 '13 at 08:45 — kooshka, Mar 21 '13 at 08:45

Daniel Hilgarth · Accepted Answer · 2013-03-21T08:56:41.593

IEntityView2 inherits the non-generic interface IEnumerable. The Select method however needs the generic version. That's why you are getting the error.

Assuming that the properties you want to access are defined on IEntity2, the following will work:

view.Cast<IEntity2>()
    .Select(c => new A1AllocationHelp1TableDTO
           {
               RecordStatus = c.RecordStatus,
               UniqueIdent = c.UniqueIdent
           })
    .ToList();

It works in VB.NET because it uses late binding. You can easily see this on the following sample:

Dim view As IEntityView2 = table.DefaultView
Dim something As List(Of A1AllocationHelp1TableDTO) = _
(From c In view
 Select New A1AllocationHelp1TableDTO With _
      {
          .RecordStatus = c.IDontExist _
      }).ToList()

I am using a property that doesn't exist (IDontExist). This code will still compile but throw an exception at runtime:

MissingMemberException: Public member 'IDontExist' on type 'IEntity2' not found.
   at Microsoft.VisualBasic.CompilerServices.Symbols.Container.GetMembers(String& MemberName, Boolean ReportErrors)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.ObjectLateGet(Object Instance, Type Type, String MemberName, Object[] Arguments, String[] ArgumentNames, Type[] TypeArguments, Boolean[] CopyBack)
   at Microsoft.VisualBasic.CompilerServices.NewLateBinding.LateGet(Object Instance, Type Type, String MemberName, Object[] Arguments, String[] ArgumentNames, Type[] TypeArguments, Boolean[] CopyBack)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

The cast is actually to view.Cast().Select(c =>... but that's exactly what I needed — kooshka, Mar 21 '13 at 09:00
@kooshka: But why the select at all? If the items in the `view` already are of the target object, all you need to do is this: `view.Cast().ToList();`. No need for creating new objects. — Daniel Hilgarth, Mar 21 '13 at 09:02
My bad. I mean Cast. view holds instances of A1AllocationHelp1Entity which is defined at runtime only, because this is in a WCF I then need to return a static defined DTO — kooshka, Mar 21 '13 at 09:11

score 0 · Answer 2 · answered Mar 21 '13 at 09:15

0

.DefaultView returns a typed view, which implements IEntityView2, but you shouldn't cast it to IEntityView2, as you then lose the generic type. So you should have done:

List<A1AllocationHelp1TableDTO> something = 
    (from c in table.DefaultView
     select new A1AllocationHelp1TableDTO
     {
         RecordStatus = c.RecordStatus,
         UniqueIdent = c.UniqueIdent
     }).ToList();

This way, the compiler knows the generic type of the view.

answered Mar 21 '13 at 09:15

Frans Bouma

8,259
1
27
28

Thanks Frans, but that doesn't work either, I still get the same error. table is of type IEntityCollection2 – kooshka Mar 21 '13 at 09:20

Linq to Objects to query LLBLGen projection

2 Answers2