Event Rule that detects changes of an attribute

[reduzent]

I created an event rule to trigger a webhook, wenever an IP address is created, deleted or updated that has a custom field set to a list of predefined values. This is the condition of the event rule:

{
    "and": [
        {
            "attr": "custom_fields.dns_a_ptr_records",
            "op": "in",
            "value": [
                "int_a",
                "ext_a",
                "int_ext_a",
                "ptr",
                "absent"
            ]
        }
    ]
}

If the the custom field dns_a_ptr_records is not set or is set to unmanaged, then the event rule does not trigger. So far, that works well. However, the event rule triggers also when I simply add a comment to the IP address.

Thus, my question: Is there way to trigger the event rule only when a certain attribute (e.g. custom field) changes?

I tried to add a comparison between the current value and the value from the pre-change object state, but apparently, I can only compare an attribute against a value, but not against another attribute.

[reduzent]

I hoped something like this would work:

{
  "and": [
    {
      "attr": "custom_fields.dns_a_ptr_records",
      "op": "in",
      "value": [
        "int_a",
        "ext_a",
        "int_ext_a",
        "ptr",
        "absent"
      ]
    },
    {
      "attr": "prev.custom_fields.dns_a_ptr_records",
      "op": "eq",
      "value": {
        "attr": "custom_fields.dns_a_ptr_records"
      },
      "negate": true
    }
  ]
}

[bitcollector1]

Welcome to the club. Maybe one day the webhook functionality will be improved. It seems like it provided little value the way it's currently implemented.