Why can rails not find a route created by a helper? -

i created member route in rails 4:

resources :line_items     post 'decrement', on: :member end 

and gave matching method in line_items controller:

def decrement     @cart = current_cart      @line_item = @cart.line_items.find_by_id(params[:id])     @line_item.decrement_quantity      respond_to |format|       if @line_item.save         format.html { redirect_to shop_path, notice: 'line item updated.' }         format.js {@current_item = @line_item}         format.json { head :ok }       else         format.html { render action: "edit" }         format.js {@current_item = @line_item}         format.json { render json: @line_item.errors, status: :unprocessable_entity }       end     end   end 

but when try make button:

<%= button_to 'x', decrement_line_item_path(item)  %> 

i error:

no route matches [post] "/carts/25" 

what gives?

your error message is:

no route matches [post] "/carts/25" 

but expecting route be: /line_items/25/decrement, not /carts/25

are line_items routes nested under carts? if so, unnest decrement action so:

# in config/routes.rb resources :carts   resources :line_items end  resources :line_items, only: []   post 'decrement', on: :member end