In CartThrob, how can I determine whether a specific product is in cart already and therefore use it in a conditional?

Question

I'm looking for a simple search of the cart contents. If a specific item I am looking for is already in cart (which I can simply define by the entry ID since the products are entries), I want to change the price applied in my add_to_cart form on the page to 0 (instead of the product's "usual" price). How can I do this? I don't think i want to do it with the cart_items_info tags from CartThrob - they have much more to them than I suspect I need.

So I'm aiming for something like this:

{if cart_contains_item_a OR cart_contains_item_b OR cart_contains_item_c}
{exp:cartthrob:add_to_cart_form return="" entry_id="{entry_id}" price="0.00"}
<input type="submit" class="button" value="Add" />
{/exp:cartthrob:add_to_cart_form}
{if:else}
{exp:cartthrob:add_to_cart_form return="" entry_id="{entry_id}" price="{cf_prod_price}"}
<input type="submit" class="button" value="Add" />
{/exp:cartthrob:add_to_cart_form}
{/if}

I'm just looking for guidance on the simplest way to determine what to include in the conditional.

Answer 1

You could use the is_in_cart tag for the conditional:

{if {exp:cartthrob:is_in_cart entry_id="{entry_id}"}}
   in cart
{if:else}
   not in cart
{/if}

Answer 2

This is what i managed to get to work. I wouldn't consider it the "right" answer without getting opinions from others, but it does work for me as intended:

{exp:cartthrob:cart_items_info entry_id="10|11|12|13" limit="1"}
{if no_results}
   INSERT MY ADD TO CART FORM WITH REGULAR PRICING
{/if}
   INSERT MY ADD TO CART BUTTON WITH DISCOUNTED PRICING
{/exp:cartthrob:cart_items_info}

In this particular case, because of how i add the items to cart, there will only ever be one of the entries indicated in the entry_id parameter present anyway, so for me, this worked as a way to loop through the entries and determine if the specified entry id was present, and if so, apply special pricing rather than regular pricing to the add to cart button/form.