saveChanges problem

Question

I am trying to delete the project from the database but I get the following exception:

"DbUpdateException was unhandled" ------------------------------------------------------------ public class Project { public Project() { Customers = new List<Customer>(); Materials = new List<Material>(); Workers = new List<Worker>(); } [Key] public long ProjectID { get; set; } public DateTime DateCreated { get; set; } public DateTime DateFinished { get; set; } public string Name { get; set; } public string Description { get; set; } public decimal Price { get; set; } //Customer TheCustomer = new Customer(); public ICollection<Customer> Customers { get; set; } public ICollection<Material> Materials { get; set; } public ICollection<Worker> Workers { get; set; } } ------------------------------------------------------------------------ if (cb_Projects.SelectedValue != null) { using (var db = new ProjectContext()) { Project p = db.Projects.Find(cb_Projects.SelectedValue); if (db.Entry(p).State == EntityState.Detached) { db.Projects.Attach(p); } p.Customers.Clear(); p.Workers.Clear(); p.Materials.Clear(); db.Projects.Remove(p); db.SaveChanges();

i guess you have some smaller/bigger-characters in there - use &gt or &lt instead of those characters — Random Dev
– Random Dev, Commented Aug 21, 2011 at 7:25
When you clear your Customers "p.Customers.Clear();" you are changing the entity state to Updated, you mustn't change the state to Updated. — Jethro
– Jethro, Commented Aug 21, 2011 at 7:37

Ladislav Mrnka · Accepted Answer · 2011-08-21 12:02:27Z

When you called this:

p.Customers.Clear(); p.Workers.Clear(); p.Materials.Clear();

You did noting because it only works if collections are populated moreover if those relations are one-to-many you will also need to delate (call Remove) on every single dependent entity. To populate those collections you must either use eager loading

long selectedValue = cb_Projects.SelectedValue; Project p = db.Projects.Include(p => p.Customers) .Include(p => p.Workers) .Include(p => p.Materials) .Single(p => p.ProjectID == selectedValue);

or mark all three properties as virtual to enable lazy loading.

Your current code should be handled by cascade delete.

This also doesn't make much sense:

if (db.Entry(p).State == EntityState.Detached) { db.Projects.Attach(p); }

You are searching for the project in the new instance of the context so it will always be loaded from the database and its state will be Unchanged.

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