Get Item from Collection by unique ID

Question

I have a collection of Contacts that inherits from CollectionBase:

public class ContactCollection : CollectionBase{
    //...
}

each contact in the collection has a unique ID:

public class Contact{
    public int ContactID{
        get;
        private set;
    }
    //...
}

I think what I would like to do is something like the following:

// get the contact by their unique [Contact]ID
Contact myPerson = Contact.GetContactById(15);

// get all contacts for the customer
ContactCollection contacts = customer.GetContacts();

// replaces the contact in the collection with the 
// myPerson contact with the same ContactID.
contacts.ReplaceAt(myPerson);

// saves the changes to the contacts and the customer
// customer.Save();

There is probably a better way...if so, please suggest it.

Answer 1

Contact contact = Contact.GetContactById(15);
ContactCollection contacts = customer.GetContacts();
contacts[contacts.IndexOf(contacts.Find(c => c.Id == contact.Id))] = contact;

---

This is a bit better...

int id = 15;
ContactCollection contacts = customer.GetContacts();
int index = users.FindIndex(c => c.Id == id)
if (index >= 0) contacts[index] = Contact.GetContactById(id);

Answer 2

For starters I would change out CollectionBase and use List<T>. CollectionBase was a 1.0 addition that is no longer needed because of Generics. Actually, you might not even need your ContactCollection class, as most of the methods you'll probably need will already be implemented in the generics implementation.

Then you can use LINQ:

var item = Collection.FirstOrDefault(x => x.Id == 15);

And if you want to keep these, then you can have your ContactCollection class just be a wrapper for the List<T> Then the code you actually have to write will be minimal as the generic will do most of the work.

Contact myPerson = Contact.GetContactById(15);

// get all contacts for the customer
ContactCollection contacts = customer.GetContacts();

// replaces the contact in the collection with the 
// myPerson contact with the same ContactID.
contacts.ReplaceAt(myPerson);

// saves the changes to the contacts and the customer
// customer.Save();

Answer 3

Why not remove the inheritance from CollectionBase, and rely on a composited Dictionary?

That way, retrieving by unique ID is close to an O(1) operation, i.e. very fast, compared to linear search over a List.

If each Contact also has a List of ContactIDs, then retrieving them from the Contacts Dictionary is also easy to do.

Some more information about Dictionaries can be found at : http://dotnetperls.com/dictionary-keys