How to update relational database TABELS?

Question

I am using Entity Framework 4.0. I am facing problem while updating data in the database. I am getting this exception :

An object with the same key al

Answer 1

Updating a detached object graph can be very difficult. (An example with only one child collection is here: https://stackoverflow.com/a/5540956/270591 If you have a grand child collection it is even more complex.)

There is no generic approach or a simple method like setting the state to Modified (it only marks scalar properties as changed) and hoping it would store all the object graph changes.

The details to consider to implement such an update:

• Does the user create new menus when a menu is added to the ceremony or does he only establish a relationship between the ceremony and an existing menu?
• Does the user delete an existing menu when a menu is removed from the ceremony or does he only release a relationship between the ceremony and the menu, but the menu should be still existing in the database (the FK must be nullable then)?
• Can the user change (scalar) menu properties in your view or can he only add menus to a ceremony or remove them without changing the menus themselves?
• The same questions apply to the grandchild collection CourseOptions of each Menu.

For the (relatively simple) case that a user in your specific ceremony Edit view...

• can modify scalar properties of the ceremony
• can remove existing menus from a ceremony that should be deleted from the database when they are removed and the related CourseOptions should be deleted as well and cascading delete for that relationship is enabled in the database
• can create and add new menus to a ceremony that should be inserted into the database
• cannot change scalar properties of existing menus
• cannot add CourseOptions to an existing Menu and cannot delete them from a Menu
• can add new CourseOptions to an new Menu (and the CourseOptions should be inserted together with the new menu)
• cannot change scalar properties of an existing CourseOption

...the code would look like this:

var ceremonyInDb = db.Ceremonies.Include(c => c.Menus)
    .Single(c => c.Id == ceremony.Id);

db.Entry(ceremonyInDb).CurrentValues.SetValues(ceremony);

foreach (var menuInDb in ceremonyInDb.Menus.ToList())
    if (!ceremony.Menus.Any(m => m.Id == menuInDb.Id))
        db.Menus.Remove(menuInDb);

foreach (var menu in ceremony.Menus)
    if (!ceremonyInDb.Menus.Any(m => m.Id == menu.Id))
        ceremonyInDb.Menus.Add(menu);

db.SaveChanges();

If some of the restrictions do not apply (i.e. the user can do more complex modifications in your view) the code will be more complex. But the basic idea is to load the object graph (root and children with Include and possibly grand children with Include(...Select(...))) from the database, compare that original graph with your new detached graph and apply changes to the original graph according to the differences to the new graph.