Allow using the same channel on multiple listeners

pgpubsub/listeners.py

@@ -2,7 +2,7 @@
 from typing import Union, Type
 
 import pgtrigger
-from pgtrigger import Trigger
+from pgtrigger import Trigger, registered
 
 from pgpubsub.channel import (
     locate_channel,
@@ -85,8 +85,16 @@ def _trigger_action_listener(channel, when, operation):
 def trigger_listener(channel: Union[Type[Channel], str], trigger: Trigger):
     channel = locate_channel(channel)
     def _trig_listener(callback):
+        triggers_already_registered = registered()
+        model_to_trigger_name = [(model, trig.name) for (model, trig) in triggers_already_registered]
+
+        if (channel.model, trigger.name) not in model_to_trigger_name:
+            # This can happen when the same channel/trigger is used
+            # for multiple listeners
+            pgtrigger.register(trigger)(channel.model)
+
         channel.register(callback)
-        pgtrigger.register(trigger)(channel.model)
+
         @wraps(callback)
         def wrapper(*args, **kwargs):
             return callback(*args, **kwargs)

pgpubsub/tests/listeners.py

@@ -47,6 +47,11 @@ def create_first_post_for_author(old: Author, new: Author):
     )
 
 
+@pgpubsub.post_insert_listener(AuthorTriggerChannel)
+def another_author_trigger(old: Author, new: Author):
+    print(f'Another author trigger')
+
+
 @pgpubsub.post_delete_listener(PostTriggerChannel)
 def email_author(old: Post, new: Post):
     author = Author.objects.get(pk=old.author_id)

pgpubsub/tests/test_core.py

@@ -2,7 +2,6 @@
 import json
 from unittest.mock import patch
 
-from django.contrib.auth.models import User
 from django.db import connection
 from django.db.transaction import atomic
 from django.db.migrations.recorder import MigrationRecorder
@@ -12,7 +11,6 @@
     listen_to_channels,
     process_notifications,
     listen,
-    NotificationRecoveryProcessor,
 )
 from pgpubsub.models import Notification
 from pgpubsub.notify import process_stored_notifications