Question

I would like to simplify this complicated logic for creating unique Track object.

def self.create_unique(p)
  f = Track.find :first, :conditions => ['user_id = ? AND target_id = ? AND target_type = ?', p[:user_id], p[:target_id], p[:target_type]]
  x = ((p[:target_type] == 'User') and (p[:user_id] == p[:target_id]))
  Track.create(p) if (!f and !x)
end

Answer 1

Here’s a rewrite of with a few simple extract methods:

def self.create_unique(attributes)
  return if exists_for_user_and_target?(attributes)
  return if user_is_target?(attributes)

  create(attributes)
end

def self.exists_for_user_and_target?(attributes)
  exists?(attributes.slice(:user_id, :target_id, :target_type))
end

def self.user_is_target?(attributes)
  attributes[:target_type] == 'User' && attributes[:user_id] == attributes[:target_id]
end

This rewrite shows my preference for small, descriptive methods to help explain intent. I also like using guard clauses in cases like create_unique; the happy path is revealed in the last line (create(attributes)), but the guards clearly describe exceptional cases. I believe my use of exists? in exists_for_user_and_target? could be a good replacement for find :first, though it assumes Rails 3.

You could also consider using uniqueness active model validation instead.