ruby on rails - How to validate the number of children records? -

i have rails 4 app 2 models.

class user    has_many :bids end  class bid   belongs_to :user end  

a user can create 1 bid per week, added following bid table

add_column :bids, :expiry, :datetime, default: datetime.current.end_of_week 

and following scopes bid model

scope :default, -> { order('bids.created_at desc') } scope :active, -> { default.where('expiry > ?', date.today ) } 

i can prevent user creating multiple bids @ controller level so:

class bidscontroller   def new     if current_user.bids.active.any?       flash[:notice] = "you have active bid. can edit here."       redirect_to edit_bid_path(current_user.bids.active.last)     else       @bid = bid.new       respond_with(@bid)     end   end end 

but best approach validating @ model level?

i've been trying set custom validation, struggling see best way set current_user available method. also, adding errors correct object?

class bid   validate :validates_number_of_active_bids   def validates_number_of_active_bids     if bid.active.where(user_id: current_user).any?       errors.add(:bid, "too much")      end   end  end 

in order maintain separation of concerns, keep current_user knowledge out of model layer. bid model has user_id attribute. also, i'd add error since validation not checking "bid" attribute on bid, rather entire bid may invalid.

class bid   validate :validates_number_of_active_bids   def validates_number_of_active_bids     if bid.where(user_id: user_id).active.any?       errors[:base] << "a new bid cannot created until current 1 expires"     end   end  end