Shopify product ids and variant ids are used commonly to form item ids in product feeds targeting ads platforms.
For example, the id generated by Google & Youtube app to synchronize into Google Merchant Center
shopify_XX_{product_id}_{variant_id}
While it is common to use just the variant id in Facebook catalog
{variant_id}
In tracking, it is very important that the tracking ids match what was submitted in the feeds, so the algorithms could have the right feedback of which items were performing well in campaigns.
This is why in all Multifeeds we provide you with options to compose any item ids formats, by interpolating texts with tokens which will pull the actual Shopify ids in) to compose both the feed item ids and the tracking ids.
Custom item ids in feeds with expression
Custom tracking ids in tracking tags
Currently the supported tokens in tracking ids include {product_id}, {variant_id} and {sku}, which is good enough for most cases. However advanced use cases call for more. For example you could be migrating your long-running high-performing products into a new store, and you want to keep all the performance history of the products by retaining the identity.
Shopify product ids and variant ids are unique. If you clone a product, the new product will have different ids
Using SKUs as item ids could be the solution as you can maintain SKUs in migrations. However SKU are used in multiple places in Shopify and might not provide the flexibility you need.
Metafields come to rescue
Metafields play important roles in Shopify product data. They are used to store any custom data of different elements, from store, customers, etc. and of course, products and variants.
To be used in tracking tags, the metafields need to be exposed to Storefront API access
And the metafield needs to be added into supported list in Multifeeds pixels and tracking setup
After that it can be selected from the token list of the item id template
Metafields can only be retrieved for published product on online store
Do note that metafields can only be retrieved via Storefront API for published products. This should not be a problem for most of the use cases as only published products can be displayed and purchased on online store (and tracked). However if you have edge cases when you want to tracking unpublished products, let us know so we can help you.