Why does the GTM adapter rewrite top-level event schema in trackEvent?

[opposable-crumbs]

I'm referencing this block here. All the top-level keys are rewritten with the prefix event. This breaks Enhanced Ecommerce tracking as it looks for the ecommerce key specifically.

Obviously I can easily override the adapter to not do this, but I'm wondering if there's even a good reason to do it in the first place. It seems like, all things being equal, the adapter should just write the schema I told it I wanted. As far as I can tell the code has been there since the introduction of the adapter and there was no explanation for it in the relevant PR.

[jherdman]

To be honest, I haven't the foggiest clue. If you look at the first commit with this code you'll see that it's pretty much been there since its inception: 86d7e12.

I'm not a GTM expert so I can't comment on why this might be desirable. I think if you can craft a path forward that offers folks a means of opting into this behaviour we can merge it.

[jherdman]

I should not that it should be done in two phases:

1. A deprecation warning indicating the new behaviour
2. A PR that will remove the old behaviour when we cut the next major

[opposable-crumbs]

Hey @jherdman, I've finally gotten around to this! I've opened the deprecation PR as you can see above. I have the commit for the new behavior ready as well, but I wasn't sure if I should wait to open that one. Don't want to flood you with PRs!

[gzurbach]

@nbenz Since your 2nd PR is not merged yet, I was wondering how you currently make it all work?

My current implementation to track purchases looks like this:

this.metrics.trackEvent({
  event: 'purchase',
  transaction_id: purchase.id,
  value: purchase.total,
  currency: purchase.currency,
  items: [
    {
      item_id: purchase.itemCode,
      item_name: purchase.label,
    },
  ],
});

Then in GTM, I had to configure 4 user-defined data layer variables:

• eventTransaction_id mapped to transaction_id (when sending to GA4)
• eventValue mapped to value
• eventCurrency mapped to currency
• eventItems mapped to items

When you say "This breaks Enhanced Ecommerce tracking as it looks for the ecommerce key specifically." are you referring to the fact that you have to map variable names manually in GA4?

[opposable-crumbs]

@gzurbach sorry, I missed this comment. I basically just implemented what I have in my PR on my local branch. You can override the existing adapter by importing it into app/metrics/google-tag-manager.js and then redefining the trackEvent method.

What you did sounds like it would also work, but I hated the idea of remapping event keys in some other system to account for some weird behavior in my JS. Much more robust to just send the correct data in the first place.