There are multiple examples on the net to implement friend/follower relationships between users. But I am unable to find a clever solution to search for the friends. Every example assumes that I selected the user objects already but it has no example how to find them prior to that.
Given an application that allows ad-hoc registration, combined with facebook/twitter login what would be the search criteria? Username does not work because finding a user registered with facebook is not possible as facebook logins won't have a usable and easy to remember username. Natural name will lead to too many "John Smiths" so I do not like the idea again. Email address sounds reasonable (as it can be extracted from facebook profile and we can ask email verification for ad-hoc registrations) but with that I have a bit of security concerns: is there a risk that someone reads the whole database storing the email addresses? Also how do I store those addresses? Do I store them in a separate class with a pointer to the user object? But then how do I prevent the "hackers" from reading the whole list?