Why has my directory search been taking so long?

Question

I was looking for performance in the REST API that I created, among other things, it returns a list of users from Active Directory based on the provided search query. Based on some of the logs I built for testing, I see that the whole process of retrieving settings (for example, LDAP search information) and getting all the search results takes less than a second:

30/08/2017 3:37:58 PM | Getting search results.
30/08/2017 3:37:58 PM | Retrieving default settings
30/08/2017 3:37:58 PM | Default settings retrieved. Creating directoryEntry
30/08/2017 3:37:58 PM | Search retrieved.
30/08/2017 3:37:58 PM | Iterating through search results.
30/08/2017 3:38:16 PM | Search results iteration complete.

However, since you can see that repeating these search results and filling out my user list takes 18 seconds. This is my code:

SearchResultCollection resultList = new DirectorySearcher(CreateDirectoryEntry())
{
    Filter = ("(&(objectClass=user) (cn=*" + SearchTerm + "*))"),
    PropertiesToLoad =
    {
        "givenName",
        "sn",
        "sAMAccountName",
        "mail"
    }
}.FindAll();

foreach (SearchResult result in resultList)
{
    ADUser thisUser = new ADUser();

    try
    {
        thisUser.Firstname = result.Properties["givenName"][0].ToString();
    }
    catch
    {
        thisUser.Firstname = "Firstname not found";
    }
    try
    {
        thisUser.Lastname = result.Properties["sn"][0].ToString();
    }
    catch
    {
        thisUser.Lastname = "Lastname not found";
    }
    try
    {
        thisUser.EmailAddress = result.Properties["mail"][0].ToString();
    }
    catch
    {
        thisUser.EmailAddress = "Email address not found";
    }

    UserList.Add(thisUser);
}

This is pretty vanilla and does nothing. Any idea why this would be so slow, or any suggestions on what I could do differently to speed it up?

UPDATE

. , :

foreach (SearchResult result in resultList)
{
    ADUser thisUser = new ADUser();

    thisUser.Firstname = result.Properties["givenName"][0].ToString();
    thisUser.Lastname = result.Properties["sn"][0].ToString();
    thisUser.EmailAddress = result.Properties["mail"][0].ToString();

    UserList.Add(thisUser);
}

. , 18 , . ( , AD , !)

Answer 1

thisUser, , , , givenName, sn / mail . , . , try/catch:

thisUser.Firstname = result.Properties.Contains("givenName")
    ? result.Properties["givenName"][0].ToString()
    : "Firstname not found";
thisUser.Lastname = result.Properties.Contains("sn")
    ? result.Properties["sn"][0].ToString()
    : "Lastname not found";
thisUser.EmailAddress = result.Properties.Contains("mail")
    ? result.Properties["mail"][0].ToString()
    : "Email address not found";

- # 6 null-coalescing, :

thisUser.Firstname = result.Properties["givenName"]?[0]?.ToString() ?? "Firstname not found";
thisUser.Lastname = result.Properties["sn"]?[0]?.ToString() ?? "Lastname not found";
thisUser.EmailAddress = result.Properties["mail"]?[0]?.ToString() ?? "Email address not found";

Answer 2

- :

foreach (SearchResult result in resultList)
            {
                ADUser thisUser = new ADUser();
                if(result.Properties["givenName"][0] != null)
                    thisUser.Firstname = result.Properties["givenName"][0].ToString();
                else
                    thisUser.Firstname = "Firstname not found";

                if(thisUser.Lastname = result.Properties["sn"][0] != null)
                    thisUser.Lastname = result.Properties["sn"][0].ToString();
                else
                    thisUser.Lastname = "Lastname not found";

                if(result.Properties["mail"][0] != null)
                    thisUser.EmailAddress = result.Properties["mail"][0].ToString();
                else
                    thisUser.EmailAddress = "Email address not found";

                UserList.Add(thisUser);
            }