context.Customers.Attach(instance, instance.Original);

…it throws an exception stating that “Value cannot be null. Parameter name: original.”

Any clue? Have you used your code in a similar fashion (i.e. GridView, DetailsView, etc.)?

Add the following line to you code in the detachableEntity – public static T Clone(T item) method to avoid this:

// copy all subclass properties.
foreach (PropertyInfo prop in item.GetType().GetProperties())
{
PropertyInfo prop2 = item.GetType().GetProperty(prop.Name);

// Check if the property can be written
if(prop2.CanWrite)
prop2.SetValue(newItem, prop.GetValue(item, null), null);
}
</code

There is one problem. The reflection code doesnt work on child relations.
I have a customer and i have orders of that customer.
I load customer with deferredloadingEnabled = false AND dataloadOptions to load the orders of that customers
Dim options As DataLoadOptions = New DataLoadOptions
options.LoadWith(Of customer)(Function(x As customer) x.orders)

When i use linq2sql without detachableEntity, i load 1 customer and 3 orders of that customer.

With detachableEntity, cust1.orders.count = 0 (i expect 3) and the cust1.original.count = 3
The problem is on this line when the property is an entityset.
prop2.SetValue(newItem, prop.GetValue(item, null), null);

So in that situation my original orders are at cust1.original.orders.original and my current orders are at cust.original.orders.

A little strange, i think

How can i fix this issue?

So either,
Creating a copy of the item is causing something in your class structure to add the new item to insert list
or
Copying every property we find is adding a new item to the instert list

I don’t think it is the recursion because your are only getting one extra per call.

How to check:

1) make DataContext public static (just for the test)
2) set break points inside the clone function.
3) evaluate [your class].DataContext.GetChangeSet() after each step

This will tell you what step is creating the insert record.
You can then find out the side efect code that is being invoked to add the insert.

Let me know what you find.

Thanks
Chris

I’ve used your DetachableEntity class as laid out here, and all works brilliantly during the update, however, there seems to be an issue when I try to delete an entity. I’m not sure if I’m doing something wrong, so I wanted to check if you had experienced any problems during deletes.

All I have done is inherit one of my entity classes from DetachableEntity in a partial class, and provided an implementation of the OnLoaded partial method as described in your article.

If I then call DeleteAllOnSubmit passing in an Expression<Func> predicate to match some criteria I don’t get any delete SQL hit my database. If I inspect the return value of the DataContext.GetChangeSet() I can see the same number of items in the Insert collection that are in the Delete section, and these items appear to be same. I guess the context is normalising this and determining that nothing needs to be deleted.

If I remove the call to base.OnDataLoaded() in the partial class (effectively removing the assignment of the cloned entity), I can run through the same code but this time the GetChangeSet result doesn’t have anything the Inserts collection, and has the correct number in the Deletes section, so the rows are correctly deleted. But of course, the update method no longer works.

My delete method is on a generic base class (and I realise that it will select the ones to delete before actually deleting them), but looks like this:

public virtual void Delete(Expression<Func> predicate)
{
if (predicate == null)
{
throw new ArgumentNullException(“predicate”);
}

/// TODO: See if there’s a way we can delete items without having to
/// perform a SELECT first.
///
var query = DataContext.GetTable().Where(predicate);
DataContext.GetTable().DeleteAllOnSubmit(query);
DataContext.SubmitChanges();
}

I then call the method with something like Delete(t => t.SomeProperty == “foo”);

Has anyone used this code and experienced anything similar?

Thanks
Ian

How do you use this class to update a collection of updating objects like List?

tumay


static void Main(string[] args)
{
  //Create new Entity
  Address home = new Address();
   //Create new data context
   AdventureWorksDataContext AW = new AdventureWorksDataContext();
   //Get Data
   home = AW.Addresses.First();
  
   // Disconnect Data Context
   AW = null;
  
   //Modify Data
   home.City = home.City + "AAA";
  
   // New Data context
   AW = new AdventureWorksDataContext();
   //Attach Entity
   AW.Addresses.Attach(home, home.original);
   //Review Changes
   ChangeSet Changes = AW.GetChangeSet();
  
   //Update Data Source
   AW.SubmitChanges();
  
   //Dispose Data Context
   AW.Dispose();
   AW = null;
   //Dispose Entity
   home = null;
  
   //Create new Data Context
   using (AW = new AdventureWorksDataContext())
   {
     //Create new Entity
     Address NewHome = AW.Addresses.FirstOrDefault(addr => addr.City.Contains("AAA"));
     //Modify Data (remove earlier changes)
     NewHome.City = NewHome.City.TrimEnd(new char[] { 'A' });
     //Submit Changes
     AW.SubmitChanges();
   }
}

I am using vs2008 and sql server 2005
I updated the usage example with this.