Question

I am trying to return a variable with values of an array of users. There are a few conditions that must be met. The user must have public_find set to true, it must not be the current_user (session variable of the user currently logged in), and it must not already be part of a friendship. The first and second conditions work perfectly. However, I am having an issue with the third part where the current_users.friendships needs to be an array of the ID values of the users where the association already exists. Any thoughts?

@users = User.find(:all, :conditions => ['
    public_find=true AND 
    id <> ? AND 
    id NOT IN (?)',
    current_user.id, current_user.friendships])

Edit:

I’ve figured out that I was missing pluck from the list. This works good now. However, if someone does not yet have a friend then current_user.friendships.pluck(:friend_id) will return NULL. I know that it is bad practice and unexpected results returned when using NOT IN and NULL. However, how do you create a condition where you can set the value to something realistic like [0] or [1] if the array returned is empty?

@users = User.find(:all, :conditions => ['
    public_find=true AND 
    id <> ? AND 
    id NOT IN (?)',
    current_user.id, current_user.friendships.pluck(:friend_id) || [0]])

EDIT AGAIN:

I got it working. However, now I want to know if this is best practice to have a statement like this. It basically is doing a check to see if the current_user.friendships.pluck(:friend_id) is empty or not. If it is then return [0]. Otherwise return an array of the user ids (foreign keyed as friend_id).

@users = User.find(:all, :conditions => ['
    public_find=true AND 
    id <> ? AND 
    id NOT IN (?)',
    current_user.id, 
    (current_user.friendships.pluck(:friend_id).empty? ? [0] : current_user.friendships.pluck(:friend_id))])

Answer 1

You can write this a little nicer ..

Show all users where public_find is true and also exclude the currently logged in user or any of their friends

ids = current_user.friendships.map(&:friend_id).concat([current_user.id])
@users = User.where(:public_find => true).where('id not in ?', ids)