feat(models): add AbstractChordCounter and update ChordCounter

- Added new abstract model `AbstractChordCounter` in `abstract.py` for Chord synchronization, including fields for `group_id`, `sub_tasks`, and `count`.
- Updated `ChordCounter` model in `generic.py` to inherit from `AbstractChordCounter`.
- Moved `group_result` method from `ChordCounter` to `AbstractChordCounter`.
- Added helper function `chordcounter_model` in `helpers.py` to return the active `ChordCounter` model.
- Updated import statements in `database.py` to use `chordcounter_model` helper function.
- Added `ChordCounterModel` attribute to `DatabaseBackend` class, and updated `create` and `get` methods to use `ChordCounterModel` instead of `ChordCounter`.

Relates to: #305

django_celery_results/backends/database.py

@@ -11,8 +11,7 @@
 from django.db.utils import InterfaceError
 from kombu.exceptions import DecodeError
 
-from ..models import ChordCounter
-from ..models.helpers import groupresult_model, taskresult_model
+from ..models.helpers import chordcounter_model, groupresult_model, taskresult_model
 from ..settings import get_task_props_extension
 
 EXCEPTIONS_TO_CATCH = (InterfaceError,)
@@ -31,6 +30,7 @@ class DatabaseBackend(BaseDictBackend):
 
     TaskModel = taskresult_model()
     GroupModel = groupresult_model()
+    ChordCounterModel = chordcounter_model()
     subpolling_interval = 0.5
 
     def exception_safe_to_retry(self, exc):
@@ -235,7 +235,7 @@ def apply_chord(self, header_result_args, body, **kwargs):
         results = [r.as_tuple() for r in header_result]
         chord_size = body.get("chord_size", None) or len(results)
         data = json.dumps(results)
-        ChordCounter.objects.create(
+        self.ChordCounterModel.objects.create(
             group_id=header_result.id, sub_tasks=data, count=chord_size
         )
 
@@ -252,10 +252,10 @@ def on_chord_part_return(self, request, state, result, **kwargs):
             # SELECT FOR UPDATE is not supported on all databases
             try:
                 chord_counter = (
-                    ChordCounter.objects.select_for_update()
+                    self.ChordCounterModel.objects.select_for_update()
                     .get(group_id=gid)
                 )
-            except ChordCounter.DoesNotExist:
+            except self.ChordCounterModel.DoesNotExist:
                 logger.warning("Can't find ChordCounter for Group %s", gid)
                 return
             chord_counter.count -= 1

django_celery_results/models/abstract.py

@@ -1,11 +1,15 @@
 """Abstract models."""
 
+import json
+
 from celery import states
+from celery.result import result_from_tuple
 from django.conf import settings
 from django.db import models
 from django.utils.translation import gettext_lazy as _
 
 from .. import managers
+from ..models.helpers import groupresult_model
 
 ALL_STATES = sorted(states.ALL_STATES)
 TASK_STATE_CHOICES = sorted(zip(ALL_STATES, ALL_STATES))
@@ -127,6 +131,53 @@ def __str__(self):
         return '<Task: {0.task_id} ({0.status})>'.format(self)
 
 
+class AbstractChordCounter(models.Model):
+    """Abstract Chord synchronisation."""
+
+    group_id = models.CharField(
+        max_length=getattr(
+            settings,
+            "DJANGO_CELERY_RESULTS_TASK_ID_MAX_LENGTH",
+            255
+        ),
+        unique=True,
+        verbose_name=_("Group ID"),
+        help_text=_("Celery ID for the Chord header group"),
+    )
+    sub_tasks = models.TextField(
+        help_text=_(
+            "JSON serialized list of task result tuples. "
+            "use .group_result() to decode"
+        )
+    )
+    count = models.PositiveIntegerField(
+        help_text=_(
+            "Starts at len(chord header) and decrements after each task is "
+            "finished"
+        )
+    )
+
+    class Meta:
+        """Table information."""
+
+        abstract = True
+
+    def group_result(self, app=None):
+        """Return the GroupResult of self.
+
+        Arguments:
+        ---------
+            app (Celery): app instance to create the GroupResult with.
+
+        """
+        return groupresult_model()(
+            self.group_id,
+            [result_from_tuple(r, app=app)
+             for r in json.loads(self.sub_tasks)],
+            app=app
+        )
+
+
 class AbstractGroupResult(models.Model):
     """Abstract Task Group result/status."""
 

django_celery_results/models/generic.py

@@ -2,13 +2,10 @@
 
 import json
 
-from celery.result import GroupResult as CeleryGroupResult
-from celery.result import result_from_tuple
-from django.conf import settings
-from django.db import models
 from django.utils.translation import gettext_lazy as _
 
 from django_celery_results.models.abstract import (
+    AbstractChordCounter,
     AbstractGroupResult,
     AbstractTaskResult,
 )
@@ -24,49 +21,13 @@ class Meta(AbstractTaskResult.Meta):
         app_label = "django_celery_results"
 
 
-class ChordCounter(models.Model):
+class ChordCounter(AbstractChordCounter):
     """Chord synchronisation."""
 
-    group_id = models.CharField(
-        max_length=getattr(
-            settings,
-            "DJANGO_CELERY_RESULTS_TASK_ID_MAX_LENGTH",
-            255),
-        unique=True,
-        verbose_name=_("Group ID"),
-        help_text=_("Celery ID for the Chord header group"),
-    )
-    sub_tasks = models.TextField(
-        help_text=_(
-            "JSON serialized list of task result tuples. "
-            "use .group_result() to decode"
-        )
-    )
-    count = models.PositiveIntegerField(
-        help_text=_(
-            "Starts at len(chord header) and decrements after each task is "
-            "finished"
-        )
-    )
-
-    class Meta:
+    class Meta(AbstractChordCounter.Meta):
+        abstract = False
         app_label = "django_celery_results"
 
-    def group_result(self, app=None):
-        """Return the GroupResult of self.
-
-        Arguments:
-        ---------
-            app (Celery): app instance to create the GroupResult with.
-
-        """
-        return CeleryGroupResult(
-            self.group_id,
-            [result_from_tuple(r, app=app)
-             for r in json.loads(self.sub_tasks)],
-            app=app
-        )
-
 
 class GroupResult(AbstractGroupResult):
     """Task Group result/status."""

django_celery_results/models/helpers.py

@@ -2,7 +2,7 @@
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 
-from .generic import GroupResult, TaskResult
+from .generic import ChordCounter, GroupResult, TaskResult
 
 
 def taskresult_model():
@@ -27,6 +27,29 @@ def taskresult_model():
         )
 
 
+def chordcounter_model():
+    """Return the ChordCounter model that is active in this project."""
+
+    if not hasattr(settings, 'CELERY_RESULTS_CHORDCOUNTER_MODEL'):
+        return ChordCounter
+
+    try:
+        return apps.get_model(
+            settings.CELERY_RESULTS_CHORDCOUNTER_MODEL
+        )
+    except ValueError:
+        raise ImproperlyConfigured(
+            "CELERY_RESULTS_CHORDCOUNTER_MODEL must be of the form "
+            "'app_label.model_name'"
+        )
+    except LookupError:
+        raise ImproperlyConfigured(
+            "CELERY_RESULTS_CHORDCOUNTER_MODEL refers to model "
+            f"'{settings.CELERY_RESULTS_CHORDCOUNTER_MODEL}' that has not "
+            "been installed"
+        )
+
+
 def groupresult_model():
     """Return the GroupResult model that is active in this project."""
     if not hasattr(settings, 'CELERY_RESULTS_GROUPRESULT_MODEL'):