ConfigurationElementCollection and Linq

 var server = ((ServerDetails) ConfigurationManager.GetSection("serverDetails")).
      ServerCollection.Cast<ServerElement>().FirstOrDefault(x => x.Name == serverName);

Using Brian Gideon's simple example of yield return in his IEnumerable<T> implementation, I was able to enumerate over my ConfigurationElementCollection.

It would look something like this (using the original question):

public sealed class ServerCollection : ConfigurationElementCollection,
    IEnumerable<ServerElement>
{
    ...

    public new IEnumerator<ServerElement> GetEnumerator()
    {
        foreach (var key in this.BaseGetAllKeys())
        {
            yield return (ServerElement)BaseGet(key);
        }
    }
}

While I was NOT getting the error:

Could not find an implementation of the query pattern for source type 'MyNamespace.ServerDetails'. 'Where' not found

...I was not able to iterate over my ConfigurationElementCollection using LINQ, either. This solution fixed my problem so that I could use LINQ to iteration over my collection.

Okay, given that it's all weakly typed, you'll need to either call Cast<> or OfType<> explicitly, or give an explicit type to the range variable. You'll also need to specify the ServerCollection property on your ServerDetails. For example:

ServerDetails servers = (ServerDetails) ConfigurationManager.GetSection("serverDetails");
var server = from ServerElement s in servers.ServerCollection
             where s.Name == serverName
             select s;