Use a proxy for special transactions in treasury app for modularity (not a clean way, but without any other solution...)

apps/note/models/__init__.py

@@ -3,12 +3,12 @@
 
 from .notes import Alias, Note, NoteClub, NoteSpecial, NoteUser
 from .transactions import MembershipTransaction, Transaction, \
-    TemplateCategory, TransactionTemplate, RecurrentTransaction
+    TemplateCategory, TransactionTemplate, RecurrentTransaction, SpecialTransaction
 
 __all__ = [
     # Notes
     'Alias', 'Note', 'NoteClub', 'NoteSpecial', 'NoteUser',
     # Transactions
     'MembershipTransaction', 'Transaction', 'TemplateCategory', 'TransactionTemplate',
-    'RecurrentTransaction',
+    'RecurrentTransaction', 'SpecialTransaction',
 ]

apps/note/models/transactions.py

@@ -6,7 +6,6 @@ from django.urls import reverse
 from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
 from polymorphic.models import PolymorphicModel
-from treasury.models import Remittance
 
 from .notes import Note, NoteClub, NoteSpecial
 
@@ -210,13 +209,6 @@ class SpecialTransaction(Transaction):
         blank=True,
     )
 
-    remittance = models.ForeignKey(
-        Remittance,
-        on_delete=models.PROTECT,
-        null=True,
-        verbose_name=_("Remittance"),
-    )
-
     @property
     def type(self):
         return _('Credit') if isinstance(self.source, NoteSpecial) else _("Debit")

apps/treasury/models.py

@@ -5,7 +5,7 @@ from django.core.exceptions import ValidationError
 from django.db import models
 from django.db.models import Q
 from django.utils.translation import gettext_lazy as _
-from note.models import NoteSpecial
+from note.models import NoteSpecial, SpecialTransaction
 
 
 class Invoice(models.Model):
@@ -110,18 +110,36 @@ class Remittance(models.Model):
         verbose_name=_("Closed"),
     )
 
+    @property
+    def transactions(self):
+        return SpecialTransaction.objects.filter(specialtransactionproxy__remittance=self)
+
     @property
     def size(self):
-        return self.specialtransaction_set.count()
+        return self.transactions.count()
 
     @property
     def amount(self):
-        return sum(transaction.total for transaction in self.specialtransaction_set.all())
+        return sum(transaction.total for transaction in self.transactions.all())
 
     def full_clean(self, exclude=None, validate_unique=True):
         ret = super().full_clean(exclude, validate_unique)
 
-        if self.specialtransaction_set.filter(~Q(source=self.type)).exists():
+        if self.transactions.filter(~Q(source=self.type)).exists():
             raise ValidationError("All transactions in a remittance must have the same type")
 
         return ret
+
+
+class SpecialTransactionProxy(models.Model):
+    transaction = models.OneToOneField(
+        SpecialTransaction,
+        on_delete=models.CASCADE,
+    )
+
+    remittance = models.ForeignKey(
+        Remittance,
+        on_delete=models.PROTECT,
+        null=True,
+        verbose_name=_("Remittance"),
+    )