Accessing another model without changing the controller

I'm having some products with a max. quantity of one per shopping cart. Instead of showing the warning when a user clicks "add to cart" when there is already 1 of these products, I'd like to redirect to the shopping cart.

To do so I'm modifying the _AddToCart.cshtml view but unfortunately the model "AddToCart" doesn't know how many products are in the shopping cart. This info is in another model. I try to avoid to change controller code since it would make upgrade to new versions more complicated in the future.

How can I access this data without changing the controller code?

If you want to " avoid to change controller code", then I think there are two options:
1) create a plugin that implements an action filter  (this is old, but probably still applies)
2) "resolve" a service in the .cshtml file, and call appropriate method

Hi NY,

Thanks for your reply. I've tried to inject the service and that worked. Many thanks!
Here is what I've done:

@inject IShoppingCartModelFactory shoppingCartServce
...

                    var shoppingCartModel = await shoppingCartServce.PrepareMiniShoppingCartModelAsync();

                    if(shoppingCartModel.Items.Count == 0)
                    {
                        => Normal button

                    }
                    else
                    {
                        => Link with "href="@Url.RouteUrl("ShoppingCart")"
                    }
...