How to Attach object to a different data context

For the last couple of days, working on my project for my studies I have struggled with this annoying issue regarding LINQ to SQL classes.

When we update an entity within a DataContext, we can simple use something like

context.Entity.Attach(updatedEntityInstance)

The proplem is that there is a catch to how my project works. I create my Entity instance within a DataContext, persist it across forms and then update my instance from another DataContext.

Simple enough, same procedure! Right? Wrong…
The Exception “ 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” is thrown…

The problem is (Strange in my opinion that it is a problem) that we are trying to update an instance which came from a disconnected DataContext.

Now there are workarounds I have read up about:

1. Use 1 instance of DataContext and persist throughout. This is firstly tedious and gave me issues regarding data "caching". An item in the Db is updated, but it does not reflect the change when we retrieve the items.
2. Right click on a table (Design View) in your dbml file, View code this then creates a partial class of that entity. This is great especially for custom validation of a specific class. In the partial class write a “Detach” method in which we set all the fk properties to their default. After this the Attach Method works. Schweeet! Not really no, I have about 16 classes in my project -> i.e. I must write 16 Detach methods!! and in all of then reset the fk property’s default. My Database schema keeps changing as well so this is super annoying!!!!
3. I took on the task to do this in reflection, took me for - wait for it - ever but db changes do not affect me now; I only have 1 global method and “MWA… It works!”

Method:

public void GenericDetach<T>(T entity) where T : class
{
    foreach (PropertyInfo pi in entity.GetType().GetProperties())
    {
        if (pi.GetCustomAttributes(typeof(System.Data.Linq.Mapping.AssociationAttribute), false).Length > 0)
        {
            // Property is associated to another entity
            Type propType = pi.PropertyType;
            // Invoke Empty contructor (set to default value)
            ConstructorInfo ci = propType.GetConstructor(new Type[0]);
            pi.SetValue(entity, ci.Invoke(null), null);
        }
    }
}

Call it as follows:

this.GenericDetach<Room>(updateRoomInstance);
db.Rooms.Attach(updateRoomInstance);

// Save room details
updateRoomInstance.RoomDescription = txtRoomDescription.Text.Trim();
…
db.SubmitChanges();