Rails add quantity to cart - ruby-on-rails

Question

I have a question:
#order_item = #order.order_items.find_or_initialize_by(product_id: params[:product_id])
I want to add one to the order item’s quantity before the .save is called.
The default value of the quantity is 0. Here is my complete code:
def create
#order_item = #order.order_items.find_or_initialize_by(product_id: params[:product_id])
respond_to do |format|
if #order_item.save
format.html { redirect_to #order, notice: 'Successfully added product to cart.' }
format.json { render :show, status: :created, location: #order_item }
else
format.html { render :new }
format.json { render json: #order_item.errors, status: :unprocessable_entity }
end
end
end
Im new to ruby and rails. How to do that? Thank you
UPDATE
<tr>
<th>Items:</th>
<td><%= #order.order_items.count %></td>
</tr>
<tr>
<th>Items</th>
<th>Title</th>
<th>Quantity</th>
<th>Unit Price</th>
<th>Subtotal</th>
<th></th>
</tr>
<% #order.order_items.each do |item| %>
<tr>
<td><%= image_tag "products/#{item.product.image_url}" %></td>
<td><%= item.product.title %></td>
<td><%= item.quantity %></td>
<td><%= print_price item.product.price %></td>
<td><%= print_price item.subtotal %></td>
<td><%= link_to 'Remove', item, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
<tr>
<th>TOTAL</th>
<td></td>
<td></td>
<td></td>
<td><%= print_price #order.total %></td>
<td></td>
</tr>
My current code is only print out total order_items in some order, what if for example each order_item quantity is 2. So I want to print out all total quantity.
<%= #order.order_items.count %>
How to do that?

Answer 1

If you have quantity attribute in order_items table, you can do that by simply assigning value to the setter, before saving.
#order_item.quantity = 1
Update:
I assume, you want order items quantities sum.
You can find total order_items quantities by
#order.order_items.sum(:quantity)
Replace your
<th>Items:</th>
<td><%= #order.order_items.count %></td>
with
<th>Items:</th>
<td><%= #order.order_items.sum(:quantity) %></td>