System.InvalidOperationException: An entity can on

问题:

am trying to update table called "Hero" , am using DataContext , here is how the codes looks like:-

//linq to sql table (automatic generated)
[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.Hero")]
    public partial class Hero : INotifyPropertyChanging, INotifyPropertyChanged
    {
          //fields methods etc..
    }

and there is my own partial class Hero ...

    public partial class Hero : IHero {
           //my fields and methods etc...

            public void Save() {
                using(GameDBDataContext db = new GameDBDataContext()) {
                    db.Heros.Attach(this, true);
                    db.SubmitChanges();
                }
        }
}

but it's throwing this :-

System.InvalidOperationException: An entity can only be attached as modified without original state if it declares a version member or does not have an update check policy.

what is the solution for this problem?

EDIT: I have tried this :-

public void Save() {
    using(GameDBDataContext db = new GameDBDataContext()) {
        db.Heros.Attach(this, db.Heros.SingleOrDefault(x => x.id == EntityID));
    }
}

and it throws :- System.NotSupportedException: An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported.

回答1:

I don't think you're using the Attach method correctly. Have you looked at this http://msdn.microsoft.com/en-us/library/bb548978.aspx ?

If the object you're passing in was created in code (rather than through deserialization) it probably won't work. If it was made via deserialization then I would recommend you try making a copy of the original object, modifying it, and using the overload which accepts a modified and unmodified entity Attach(Entity old, Entity new).