fix(alerts): Fix Slack custom template notification issues

- Fix KeyError when using custom template in alert notifications
- Prevent default template fields from appearing alongside custom template

Changes:
- Use .get() with fallback for selector/op/value in render_template()
- Restructure Slack destination to send only custom template when set

Author: JHZLO

redash/destinations/slack.py

@@ -23,31 +23,35 @@ def icon(cls):
 
     def notify(self, alert, query, user, new_state, app, host, metadata, options):
         # Documentation: https://api.slack.com/docs/attachments
-        fields = [
-            {
-                "title": "Query",
-                "type": "mrkdwn",
-                "value": "{host}/queries/{query_id}".format(host=host, query_id=query.id),
-            },
-            {
-                "title": "Alert",
-                "type": "mrkdwn",
-                "value": "{host}/alerts/{alert_id}".format(host=host, alert_id=alert.id),
-            },
-        ]
-        if alert.custom_body:
-            fields.append({"title": "Description", "value": alert.custom_body})
         if new_state == "triggered":
-            if alert.custom_subject:
-                text = alert.custom_subject
-            else:
-                text = alert.name + " just triggered"
             color = "#c0392b"
         else:
-            text = alert.name + " went back to normal"
             color = "#27ae60"
 
-        payload = {"attachments": [{"text": text, "color": color, "fields": fields}]}
+        if alert.custom_body:
+            if alert.custom_subject:
+                text = alert.custom_subject
+            else:
+                text = alert.name + (" just triggered" if new_state == "triggered" else " went back to normal")
+            payload = {"attachments": [{"text": text, "color": color, "mrkdwn_in": ["text"], "fields": [{"value": alert.custom_body}]}]}
+        else:
+            fields = [
+                {
+                    "title": "Query",
+                    "type": "mrkdwn",
+                    "value": "{host}/queries/{query_id}".format(host=host, query_id=query.id),
+                },
+                {
+                    "title": "Alert",
+                    "type": "mrkdwn",
+                    "value": "{host}/alerts/{alert_id}".format(host=host, alert_id=alert.id),
+                },
+            ]
+            if new_state == "triggered":
+                text = alert.name + " just triggered"
+            else:
+                text = alert.name + " went back to normal"
+            payload = {"attachments": [{"text": text, "color": color, "fields": fields}]}
 
         try:
             resp = requests.post(options.get("url"), data=json_dumps(payload).encode("utf-8"), timeout=5.0)

redash/models/__init__.py

@@ -1071,9 +1071,9 @@ def render_template(self, template):
             "ALERT_NAME": self.name,
             "ALERT_URL": "{host}/alerts/{alert_id}".format(host=host, alert_id=self.id),
             "ALERT_STATUS": self.state.upper(),
-            "ALERT_SELECTOR": self.options["selector"],
-            "ALERT_CONDITION": self.options["op"],
-            "ALERT_THRESHOLD": self.options["value"],
+            "ALERT_SELECTOR": self.options.get("selector", self.options.get("column", "")),
+            "ALERT_CONDITION": self.options.get("op", ""),
+            "ALERT_THRESHOLD": self.options.get("value", ""),
             "QUERY_NAME": self.query_rel.name,
             "QUERY_URL": "{host}/queries/{query_id}".format(host=host, query_id=self.query_rel.id),
             "QUERY_RESULT_VALUE": result_value,