Get User's ID for inserting into a lookup field

Question

So I can use the PeopleManager to get a user's profile but I can't figure out how to get the correct ID I need in order to add a new list item to a list and populate a look-up type field with that specific user's information.

After an item is inserted I can get that value using the FieldUserValue but how do I determine it before?

This is using COM in C# and SharePoint 2013 Online.

Answer 1

From a COM solution you can fetch data of the User's only by

/site/test/_vti_bin/userprofileservice.asmx

web service. So you can user the following code to fetch data:

  UserProfileService tmpUserProfileService = new UserProfileService();
  tmpUserProfileService.Credentials = new NetworkCredential("ADMIN", "PASSWORD", "DOMAIN");
  PropertyData[] properties =tmpUserProfileService.GetUserProfileByName(@"DOMAIN\USER");            
  for (int i = 0; i < properties.Length; i++)
  {
       Console.WriteLine(properties[i].Name);
       Console.WriteLine(properties[i].Value);
  }
  Console.Read();

Reference: User Profile Server