class CreateOrders < ActiveRecord::Migration[5.1]
  def change
    create_table :orders do |t|
      t.timestamps
    end
  end
end

class CreateOrderItems < ActiveRecord::Migration[5.1]
  def change
    create_table :order_items do |t|
      t.integer :order_id, index:true
      t.integer :product_id, index:true
      t.integer :amount
      t.timestamps
    end
  end
end

class CreateProducts < ActiveRecord::Migration[5.1]
  def change
    create_table :products do |t|
      t.text :name
      t.integer :family_id, index:true
      t.timestamps
    end
  end
end

class CreateFamilies < ActiveRecord::Migration[5.1]
  def change
    create_table :families do |t|
      t.text :name
      t.timestamps
    end
  end
end

class Family < ApplicationRecord
  has_many :products
end

class Order < ApplicationRecord
  has_many :order_items
  has_many :products, through: :order_items
end

class OrderItem < ApplicationRecord
  belongs_to :order
  belongs_to :product
end

class Product < ApplicationRecord
  belongs_to :family
  has_many :order_items
end

irb(main):015:0> Order.joins(:order_items).joins(:products).where("products.family_id":2).where("orders.created_at": [(Time.now).to_date..(Time.now + 1.day).to_date]).count
   (0.6ms)  SELECT COUNT(*) FROM "orders" INNER JOIN "order_items" ON "order_items"."order_id" = "orders"."id" INNER JOIN "order_items" "order_items_orders_join" ON "order_items_orders_join"."order_id" = "orders"."id" INNER JOIN "products" ON "products"."id" = "order_items_orders_join"."product_id" WHERE "products"."family_id" = ? AND ("orders"."created_at" BETWEEN '2018-04-20' AND '2018-04-21')  [["family_id", 2]]
=> 3