My name
is
Jon Skeet

Use dictionary instead of List get ith entry

Perhaps I am just having my dumb moment right now. I have the following:

List<DirectoryEntry> list = new List<DirectoryEntry>();
List.Add(startEntry);
int i=0;
while(i < list.Count) {
    DirectoryEntry entry = list[i];
    foreach(DirectoryEntry child in GetChildEntries(entry)) {
        if(!list.Contains(child)) // Do not add if entry already in list!
            list.Add(child);
    }
}

This does not work because Contains somehow returns false for two directoryEntries that point to the same AD object.

So I thought to make a Dictionary from that and store the distinguishedName along with the entry:

Dictionary<string,DirectoryEntry> list = new Dictionary<string,DirectoryEntry>();
List.Add(startEntry.Properties["distinguishedName"].Value,startEntry);
int i=0;
while(i < list.Count) {
    DirectoryEntry entry = list[i]; // Does not work, because the index is a string here.
                                    // How to get the ith entry from the dictionary?
    foreach(DirectoryEntry child in GetChildEntries(entry)) {
        var dn = child.Properties["distinguishedName"].Value;
        if(!list.ContainsKey(dn)) list.Add(dn,child);
    }
}

The question, as stated in the code comment:

How to get the ith entry from the dictionary?

Well you can use list.ElementAt(i) to get the i^th element in the order they happen to be returned by the dictionary - but there's no guarantee as to what order that is, or that it will stay consistent over time. I would strongly recommend avoiding thinking of a dictionary has having any concept of order.

It seems to me that you just need to iterate over the dictionary though:

foreach (var entry in list)
{
    ...
}

That leads to another problem though, which is that you're modifying the collection you're iterating over while you're iterating over it, which will fail. You might want to consider creating a new dictionary while you're iterating, and then add all the entries to the original one afterwards.

It's unclear whether you really want a dictionary or not though. We don't know what you're really trying to achieve - there are many different options here.

EDIT: If you want to flatten, you could do something like:

var entries = new Dictionary<string, DirectoryEntry>();
var queue = new Queue<DirectoryEntry>();
queue.Enqueue(startEntry);
while (queue.Count > 0)
{
    var candidate = queue.Dequeue();
    string key = candidate.Properties["distinguishedName"].Value;
    if (!entries.ContainsKey(key))
    {
        entries[key] = candidate;
        foreach (var child in GetChildEntries(candidate))
        {
            queue.Enqueue(child);
        }
    }
}

You could "hide" the foreach loop by creating your own EnqueueAll extension method on Queue<T>, if you wanted.

This feels to me like simpler code to understand than iterating over a collection you're still adding to.

EDIT: And if you don't need to look up by distinguished name later, you can use a HashSet<DirectoryEntry> with a custom equality comparer:

var entries = new HashSet<DirectoryEntry>(new DirectoryEntryEqualityComparer());
var queue = new Queue<DirectoryEntry>();
queue.Enqueue(startEntry);
while (queue.Count > 0)
{
    if (entries.Add(candidate))
    {
        foreach (var child in GetChildEntries(candidate))
        {
            queue.Enqueue(child);
        }
    }
}

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