How to restrict current_user from adding more than 3 order_items to a order per time period?

Question

I'm building a store in Rails that has a specific sales model. I need to allow a user to add only 3 items to his order per 30 days. The 30 days counter should start upon adding the first order_item. Once 30 days expires, user would be able to add 3 orders. If 30 days didn't pass and for an example, user adds two order_items he would still be allowed to add one more order_item within 30 days. So as well if user tries to add more then 3 items to show an error message and disregard saving of the order_items to current_user's order.

I have products, orders, order_items, users. I guess that I should add something to user model but I'm not sure what.

order_items_controller.rb

def create
    @order = current_order
    @order_item = @order.order_items.new(order_item_params)
    @order.user_id = current_user.id
    @order.save
    session[:order_id] = @order.id

  respond_to do |format|
    format.js { flash[:notice] = "ORDER HAS BEEN CREATED." } 
  end
  end
private
  def order_item_params
    params.require(:order_item).permit(:quantity, :product_id, :user_id)
  end
end

user.rb

class User < ActiveRecord::Base
  has_many :identities, dependent: :destroy
  has_many :order
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :omniauthable, :invitable, :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable
end

order_item.rb

class OrderItem < ActiveRecord::Base
  belongs_to :product
  belongs_to :order

  validates :quantity, presence: true, numericality: { only_integer: true, greater_than: 0 }
  validate :product_present
  validate :order_present

  before_save :finalize

  def unit_price
    if persisted?
      self[:unit_price]
    else
      product.price
    end
  end

  def total_price
    unit_price * quantity
  end

private
  def product_present
    if product.nil?
      errors.add(:product, "is not valid or is not active.")
    end
  end

  def order_present
    if order.nil?
      errors.add(:order, "is not a valid order.")
    end
  end

  def finalize
    self[:unit_price] = unit_price
    self[:total_price] = quantity * self[:unit_price]
  end
end

order.rb

class Order < ActiveRecord::Base
  belongs_to :order_status
  has_many :order_items
  before_create :set_order_status
  before_save :update_subtotal

  def subtotal
    order_items.collect { |oi| oi.valid? ? (oi.quantity * oi.unit_price) : 0 }.sum
  end
private
  def set_order_status
    self.order_status_id = 1
  end

  def update_subtotal
    self[:subtotal] = subtotal
  end
end

carts_controller.rb

class CartsController < ApplicationController
  def show
    @order_items = current_order.order_items
  end

routes.rb

resources :order_items, only: [:create, :update, :destroy, :new]

form.html.erb

<%= form_for OrderItem.new,  html: {class: "add-to-cart"}, remote: true do |f| %>


        <div class="input-group">
          <%= f.hidden_field :quantity, value: 1, min: 1 %>
          <div class="input-group-btn">
            <%= f.hidden_field :product_id, value: product.id %>
            <%= f.submit "Add to Cart", data: { confirm: 'Are you sure that you want to order this item for current month?'}, class: "btn btn-default black-background white" %>
          </div>
        </div>
      <% end %>
    </div>

Answer 1

I would add a begin_date and a order_counter to user model. Every time you add an order, look if the begin_date is more than 30 days ago, then set the begin_date to the actual date. If the begin_date is less than 30 days ago, increase the counter. And if the counter ist already 3 refuse the order.

You can add the columns to the user table by the command line argument

rails generate migration AddOrderCounterToUser

This will create a class in db/migrations:

class AddPartNumberToProducts < ActiveRecord::Migration
  def change
    add_column :users, :begin_date, :date
    add_column :users, :order_counter, :integer 
  end
end

Add the additional attributes in your UserController to permit them in user_params .

Then change the create method in your OrderItemController

def create
  now = Date.today
  success = false
  if current_user.begin_date && ((now - 30) < current_user.begin_date)
     if current_user.order_counter >= 3
        # deal with the case that order should not be created, 
        # for example redirect.
     else
       current_user.order_counter += 1
       current_user.save
       success = true
     end
  else 
    current_user.order_counter = 1
    current_user.begin_date = now
    current_user.save
    success = true
  end
  if success
    @order = current_order
    @order_item = @order.order_items.new(order_item_params)
    @order.user_id = current_user.id
    @order.save
    session[:order_id] = @order.id

    respond_to do |format|
      format.js { flash[:notice] = "ORDER HAS BEEN CREATED." } 
    end
  else 
    respond_to do |format|
      format.js { flash[:notice] = "CREATION NOT POSSIBLE." } 
    end
  end
end

You can also put the checking code in a method in the user model, that would be cleaner.

Answer 2

Generally, when you don't want to create an element in rails under certain circumstances, you should choose to handle the situation via validators.

You could take a nesting approaches here: Nest your OrderItem routes under Order (you can find further information about nesting in the Rails Guides about Nested Routing )

You should start by adding a new database column first_item_added_at to you Order model

rails generate migration AddFirstItemAddedAtToOrder

class AddFirstItemAddedAtToOrder < ActiveRecord::Migration
  def change
    add_column :orders, :first_item_added_at, :date
  end 
 end

When nesting, you would create a new OrderItem via the route

POST /orders/:id/order_items

Then, you have to add a validator to your OrderItem model

class OrderItem < ActiveRecord::Base
    validate :only_3_items_in_30_days


  private

  def only_3_items_in_30_days
    now = Date.new
    days_since_first = now - order.first_item_added_at

    if order.order_items.count > 2 && days_since_first < 30
      errors.add(:base, 'only 3 items in 30 days are allowed')
    end
    true      # this is to make sure the validation chain is not broken in case the check fails
  end
end

Now your controller only needs to create a new item and save it

def create
  @item = OrderItem.new(item_params)
  if @item.save
     render <whatever_you_want_to_render>
  else
    # @item will contain the errors set in the model's validator
    render <error_reaction>
  end
end

private

def item_params
  params.require(:order_item).permit(
    :attribute_1,
    :attribute_2,
    :order_id       # << this one is very important
  )
end

If you don't wish to nest OrderItem , than the model still remains the same, but your controller would look like:

def create
  @item = OrderItem.new(order_item_params)
  session[:order_id] = current_order.id

  if @item.save
    respond_to do |format|
      format.js { flash[:notice] = "ORDER HAS BEEN CREATED." } 
    end
  else
    render <handling for error>
  end 
end

private
def order_item_params
  base_params = params.require(:order_item)
                      .permit(:quantity, :product_id, :user_id)
  base_params.merge(order: current_order)
 end

Please note, that I added current_order.id to your order_item_params method.

EDIT: replaced order_id: current_order.id by order: current_order to provide the relation to the new OrderItem before it is actually saved