Question

I’m getting a InvalidOperationException when trying to run this code:

database.Produkts.SingleOrDefault<Produkt>(x => x.Kod == "123")

It only occurs when the Kod property has an override modifier.
I need it this way because the entity class is derived from another class that resides in a separate assembly.

Here’s how the classes are defined:

The base class:

namespace Interfaces.Model
{
    [DataContract(Name = "Produkt", Namespace = "")]    
    public class Produkt
    {
        [DataMember]        
        public virtual string Kod { get; set; }

...

The class generated by Linq:

namespace DAL.Linq
{

  [Table(Name="dbo.Produkt")]
  public partial class Produkt : INotifyPropertyChanging, INotifyPropertyChanged
  {
        [Column(Storage="_Kod", DbType="NVarChar(50) NOT NULL", CanBeNull=false)]
        public override string Kod
        {
            get
            {
                return this._Kod;
            }
            set
            {
                if ((this._Kod != value))
                {
                    this.OnKodChanging(value);
                    this.SendPropertyChanging();
                    this._Kod = value;
                    this.SendPropertyChanged("Kod");
                    this.OnKodChanged();
                }
            }
        }
...

And the second part of the definition:

namespace DAL.Linq
{
    [DataContract(Name = "Produkt", Namespace = "")]    
    partial class Produkt : Interfaces.Model.Produkt
    {
    }
}

Now retrieving all the instances from the database (without the filter/where caluse) will work just fine. It’s only that building a predicate that includes the overridden property will not.

I assume that it’s some kind of a problem related to retrieving the property’s attributes with reflection as the exception gets thrown from the method GetDataMember of the System.Data.Linq.Mapping.MetaType class.

My real question is if this is a Linq bug or can I somehow make Linq recognize this property to attribute mapping?

Answer 1

Found a workaround here: http://social.msdn.microsoft.com/Forums/en-US/linqprojectgeneral/thread/016ad28b-f813-4f26-9e70-2265a1943bad

In short: the query works after modifying it like this:

database.Produkts.SingleOrDefault<Produkt>(x => ((DAL.Linq.Produkt)x).Kod == "123")

The cast should be obsolete (and f.i. Resharper marks it as such) but evidently it does make a difference when reflection methods are applied to the resulting Expression objects.