Wrong object added to ObjectContext (_addedEntityStore)

Question

I have a wizard in my asp.net MVC application which is built upon this SoG - RESTFUL wizard guide.

In order to understand the problem I will first explain the situation below. For this I will use a dummy situation, we try to create a person with an address. Again, this is just a dummy situation!

The situation

At start, the object (person) to be created and saved using the wizard is created as a blank object (person) and will be filled during the wizard 'stage'. In between the various wizard steps the person object is stored in the SESSION and retrieved with a key. This object has a relation with a sub-object. For example, an address. This address can either be retrieved from a DB using a dropdown-menu in the wizard _or_ can be created in the wizard itself. This means that at creation I will create an empty address-object so we have the following initialization:

Persons p = new Persons();
p.Addressess = new Addressess()

This object is passed to the FormViewModel and used in the Wizard Form. Here I have a drop-down enabling to choose: (1) *create new address for person", which fills the passed empty-address object with data using the usual ways (TryUpdateModel()) and (2) "address x", addresses to select from your DB.

Selecting one of the addresses in the dropdown will, in the controller POST method, retrieve this object from DB and couple it to the person.Addresses. In code:

p.Addresses = repository.GetContactByID(id);

The problem

Everything works fine while running through the wizard pages. The problem occurs when I call the savechanges(). While in a final overview the complete object to be added is shown correctly (person info + address info as selected / passed), also an empty address is saved to the database.

repository.SaveChanges();

This will try to add an empty Addresses to the DB which will introduce a ModelState error since Addresses have some non-nullable's which are not set for the empty object.

** My current idea ** My current thinking is that the empty object created at start for the blank object is somehow placed in added state (objectcontext) when I first couple it to person.Addresses. Can this be the case? What would be the correct way to do what I want? Can I manually delete things from the object context _addedEntityStore ?

Additional Info

Selection of an address in the dropdown will force a form.submit to the POST controller method and consecutively it will reload the form with updated selection info and the input fields for the new address (in case a new one is wanted) set to "disabled" so you only see the info but cannot edit an existing address.

Also, only one objectContext is used which is saved in the SESSION.

Answer 1

Any reason you can't just leave p.Addressess as null when you first create a Persons object and only add a new Address if that's what they select in the wizard?

(And BTW why the odd pluralization? Do they have one address or several?)

The other issue you will encounter is that you will be loading existing addresses in one context and saving them in another (assuming you are using a context per request approach) - you'll need to detach the existing addresses from one context they were loaded in and attach them to the context used to save Person at the end of the wizard.

It might be easier to include a separate AddressNew and an AddressExisting object in the Session state (one or the other is null). At the end, if AddressNew is present, add it to the Person and save changes. If AddressExisting is present, attach it to the context, add it to the Person and save changes.

Answer 2

Although Hightechrider is right about using an object context for every unit of work I post the simple solution I used for now. When you somehow (forced, chosen, whatever) have your object context stored in SESSION you can solve the above problem simply by calling:

repository.Detach(person.Addresses) 

Which will detach the old object from the context (not saved yet to DB). And after detaching, attach the new object you want to have it linked to.

person.Addresses = repository.GetAddressByID(id);
// or
person.Addresses = new Addresses();

Though I do recommend rewriting your wizard if you need to do this and have the time and power :).

edit

note that Detach only detaches the object supplied, not its related objects (!).