Bring back cached_render_for_web (#262)

engine/apps/alerts/migrations/0004_auto_20220711_1106.py

@@ -4,18 +4,25 @@ from django.db import migrations
 
 
 class Migration(migrations.Migration):
+    """
+    The previous version of this migration removes two fields:
+    cached_render_for_web and active_cache_for_web_calculation_id.
+    Now it doesn't do anything because it can be very slow and even fail on write heavy alertgroup table.
+    This migration was released in version 1.0.7, so in order to bring back these fields in the later version
+    there's a 0005 migration. Please see the next migration in alerts: 0005_alertgroup_cached_render_for_web.py
+    """
 
     dependencies = [
         ('alerts', '0003_grafanaalertingcontactpoint_datasource_uid'),
     ]
 
     operations = [
-        migrations.RemoveField(
-            model_name='alertgroup',
-            name='active_cache_for_web_calculation_id',
-        ),
-        migrations.RemoveField(
-            model_name='alertgroup',
-            name='cached_render_for_web',
-        ),
+        # migrations.RemoveField(
+        #     model_name='alertgroup',
+        #     name='active_cache_for_web_calculation_id',
+        # ),
+        # migrations.RemoveField(
+        #     model_name='alertgroup',
+        #     name='cached_render_for_web',
+        # ),
     ]

engine/apps/alerts/migrations/0005_alertgroup_cached_render_for_web.py

@@ -0,0 +1,45 @@
+# Generated by Django 3.2.13 on 2022-07-20 09:04
+
+from django.db import migrations, models, OperationalError
+
+
+class AddFieldIfNotExists(migrations.AddField):
+    """
+    Adds a field and ignores "duplicate column" error in case the field already exists.
+    When migrating back it will not delete the field.
+    """
+
+    def database_forwards(self, app_label, schema_editor, from_state, to_state):
+        try:
+            super().database_forwards(app_label, schema_editor, from_state, to_state)
+        except OperationalError:
+            pass
+
+    def database_backwards(self, app_label, schema_editor, from_state, to_state):
+        pass
+
+
+class Migration(migrations.Migration):
+    """
+    This migration tries to create two fields cached_render_for_web and active_cache_for_web_calculation_id.
+    In case these fields already exist, this migration will do nothing.
+    In case the database was already affected by the previous version of the 0004 migration,
+    it will recreate these fields.
+    """
+
+    dependencies = [
+        ('alerts', '0004_auto_20220711_1106'),
+    ]
+
+    operations = [
+        AddFieldIfNotExists(
+            model_name='alertgroup',
+            name='cached_render_for_web',
+            field=models.JSONField(default=dict),
+        ),
+        AddFieldIfNotExists(
+            model_name='alertgroup',
+            name='active_cache_for_web_calculation_id',
+            field=models.CharField(default=None, max_length=100, null=True),
+        ),
+    ]

engine/apps/alerts/models/alert_group.py

@@ -299,6 +299,10 @@ class AlertGroup(AlertGroupSlackRenderingMixin, EscalationSnapshotMixin, models.
         related_name="dependent_alert_groups",
     )
 
+    # cached_render_for_web and active_cache_for_web_calculation_id are deprecated
+    cached_render_for_web = models.JSONField(default=dict)
+    active_cache_for_web_calculation_id = models.CharField(max_length=100, null=True, default=None)
+
     last_unique_unacknowledge_process_id = models.CharField(max_length=100, null=True, default=None)
     is_archived = models.BooleanField(default=False)