I have a User object, and an Alliance object, where User has_many :alliances, and Alliance belongs_to :user. I want to get a list of users, but exclude those users with whom the current_user already has an active alliance (if the user already has an alliance, the :pending field will be false).
Here's a concrete example. Suppose our users are Joe, Bob and Jill. Joe and Jill are active allies, so Joe.alliances will include Jill, and Jill,alliances will include Joe. I want a list of all users that exclude alliances for the current user, so if Joe is current_user, then I want an array of User objects that does not include Jill, but does include Bob.
In code, what I have so far:
# Get all users
user_list = User.all
# Get alliances that are not pending
active_alliances = current_user.where(:pending => false)
Now, I was thinking of using this tip to exclude from user_list the active_alliances. So, what I need to do is extract from active_alliances a single-dimensional array with nothing other than a list of user_ids. I'm thinking something like:
# Select just the :ally field (which contains the user_id of the ally)
alliance_id_list = current_user.all(:select => "ally")
This last isn't quite what I want, because it gives me a hash. Now, I could just iterate through the hash, but I'm thinking that might not be the best way. Is there a direct method to do this? Perhaps by setting a negative conditional for the query? Thanks.
Update: See this question for more details on how to solve this problem; it can be used in connexion with the .collect method suggested below.
