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I'm creating a product page for a product with multiple variants. In this case the variant represents a different size (with unique SKU, stock, etc..).

It's laid out like so (don't mind the ugly styling):

product box

I don't want to pre-select a size option because I want to avoid people adding the wrong product to their cart.

In the template there's a hidden field with the purchasableId of the variant. The value attribute starts empty and when people click one of the options it is set to the corresponding id.

<input type="hidden" name="purchasableId" value="">

However, when people click 'Add to cart' right away, without selecting a size the following Craft\Exception is shown:

Not a purchasable ID

How can I customize this error message to notify the customer that they have to select a size option?

I could of course solve this problem by using javascript but that doesn't seem very solid to me. So is there a way of validating the stuff added to the cart in the back-end and getting something like a JSON response?

  • 1
    Just an opinion, but this seems to me like exactly the sort of thing you would validate on the front end using js/css/whatever – aw04 Dec 23 '16 at 20:34
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Well, if you submit to your add to cart form via ajax, you will already get a json response - with an error - you can simply grab that error, test for Not a purchasable ID and then change the text to whatever you want.

If you're submitting in a non ajax fashion, you won't get a JSON response no matter what clearly.

I agree with the comment above - I'd generally handle this in front end JS, by disabling the add to cart until a size is selected. And I guess if you're allowing your site to use no-js, then in that case I would probably just pre-select the most popular option (Medium, presumably).

You can also write a plugin that listens to https://craftcommerce.com/docs/events-reference#commerce_cart.onbeforeaddtocart and does whatever validation you need, and returns a response any way you want, including via JSON (i.e. $this->returnJson(["success"=>true]); or e.g. $this->returnErrorJson($errors); where $errors holds your validation errors...)

  • Actually, when sending the form via ajax, you will get a 500 Internal Server Error if you don't add the purchasableId to the query. So I will have to validate this before actually sending anything to the back-end. – Floriskoch Dec 26 '16 at 12:41
  • Well, that's a bug you should report to support@craftcommerce.com then - the intended behaviour would definitely not be a 500 internal server error. E.g an incorrect purchasableId gives an error...and a missing one obviously should too. Looking at the cart controller it does seem like it isn't handling a missing Id indeed.... – Jeremy Daalder Dec 26 '16 at 21:59

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