the error message for using dimensions within a non-aggregate metric isn't clear

How I got here…

I tried to aggregate a dimension within a non-aggregate metric definition. This failed, because non-aggregate metrics can only take in other aggregate metrics.

^I think that this behaviour is fine: forcing people to write out metrics instead of doing dimension aggregations in the metric’s sql is pretty acceptable and makes it super clear what the restrictions of these non-aggregate metrics are. It’s also clearly explained in our docs that this is the behaviour to expect.

buuuuuut, it took me like 3 tries to figure out what was going wrong.

This was the yaml I had:

- name: email_campaign_id
        description: The ID of the email campaign.
        tests:
          - unique
          - not_null
        meta:
          metrics:
            campaign_spam_report_rate:
              description: "Spam report rate is the ratio of emails reported as spam out of the emails that were delivered."
              type: number
              sql: "(SUM(${total_unique_spam_reports}) / NULLIF(SUM(${total_unique_deliveries}), 0))"

This was the error I received:

This was the fix I needed to make:

- name: total_unique_spam_reports
      meta:
          metrics:
            sum_of_total_unique_spam_reports:
              type: sum

- name: total_unique_deliveries
      meta:
          metrics:
            sum_of_total_unique_deliveries:
              type: sum
  
- name: email_campaign_id
        description: The ID of the email campaign.
        tests:
          - unique
          - not_null
        meta:
          metrics:
            campaign_spam_report_rate:
              description: "Spam report rate is the ratio of emails reported as spam out of the emails that were delivered."
              type: number
              sql: "(${sum_of_total_unique_spam_reports}) / NULLIF(${sum_of_total_unique_deliveries}, 0)"

The error message should have a better description of what’s going wrong. Specifically, it should say something about the metric that’s erroring and the fact that it’s a non-aggregate metric. It should potentially link to the docs if that’s possible too!

e.g.

Error: `campaign_spam_report_rate` is a non-aggregate metric. It can only be defined using aggregate metrics, not dimensions. See the docs for how to build non-aggregate metrics: https://docs.lightdash.com/references/metrics#non-aggregate-metrics

[owlas]

Powerful error message @TuringLovesDeathMetal ! 🚀

[stale[bot]]

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