This has to be a frequent question, but not on SO yet, so it seems. I am using Linq to SQL for an application that allows a variety of data changes to my in-memory model, and the changes will then get placed into a queue for asynchonous processing. So, I am not worried about updates (yet).
Changes to various parts of the data can be made through modal popups on the web page. Some are grid-based, others are just attributes.
I am running into a problem with changes not surviving postback cycles. Obviously, I don’t want to persist anything to the database until all changes are made and the user submits the page.
The route that I have chosen so far is:
- I disabled deferred loading
- I create a [serializable] partial class for my root object
- I put the thing into the session and retrieve it in the onload event
This seems to work in principle. However, when I try to update some of the children’s properties after retrieving the object from the session
p.PhysicianSpecialties[0].physician_specialty_code =
ddlSpecialty.SelectedItem.Value;
I get this error:
Operation is not valid due to the current state of the object.
The error is caused by this method call in the generated Linq setter method:
this.SendPropertyChanging();
Other properties get updated just fine:
p.PhysicianNames[0].first_name = txtFirstName.Text.ToUpper();
This does not cause an error.
My questions: Am I fundamentally on the wrong track? Is there a better way of doing this? What causes the error?
Update:
The exception is ‘System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException’. I think I am on to something, but I don’t know the solution yet.
I got the solution from MSDN. The issue is, and it is explained better in this thread than I can do it, that one cannot change an association unilaterally, but has to do it on both ends, by assigning a new child object, not just by a changing the id:
p.PhysicianSpecialties[0].PhysicianSpecialtyLookup =
db.PhysicianSpecialtyLookups.Single(c =>
(c.physician_specialty_code == ddlSpecialty.SelectedItem.Value));