def invite(user)
      return false if friendshiped_with?(user) or user == self or blocked?(user)
      pending_friend_ids << user.id
      user.pending_inverse_friend_ids << self.id
      self.save && user.save
    end
def invite(user)
      return false if friendshiped_with?(user) or user == self or blocked?(user)
      pending_friend_ids << user.id
      user.pending_inverse_friend_ids << self.id
      self.save && user.save
    end
suggest a user to become a friend. If the operation succeeds, the method returns true, else false