feat(automatic-exchange-rates): add "Single exchange rate" where only one exchange rate is added and updated to avoid db clutter

app/apps/currencies/exchange_rates/fetcher.py

@@ -203,21 +203,63 @@ class ExchangeRateFetcher:
 
                 if provider.rates_inverted:
                     # If rates are inverted, we need to swap currencies
-                    ExchangeRate.objects.create(
-                        from_currency=to_currency,
-                        to_currency=from_currency,
-                        rate=rate,
-                        date=timezone.now(),
-                    )
+                    if service.singleton:
+                        # Try to get the last automatically created exchange rate
+                        exchange_rate = (
+                            ExchangeRate.objects.filter(
+                                automatic=True,
+                                from_currency=to_currency,
+                                to_currency=from_currency,
+                            )
+                            .order_by("-date")
+                            .first()
+                        )
+                    else:
+                        exchange_rate = None
+
+                    if not exchange_rate:
+                        ExchangeRate.objects.create(
+                            automatic=True,
+                            from_currency=to_currency,
+                            to_currency=from_currency,
+                            rate=rate,
+                            date=timezone.now(),
+                        )
+                    else:
+                        exchange_rate.rate = rate
+                        exchange_rate.date = timezone.now()
+                        exchange_rate.save()
+
                     processed_pairs.add((to_currency.id, from_currency.id))
                 else:
                     # If rates are not inverted, we can use them as is
-                    ExchangeRate.objects.create(
-                        from_currency=from_currency,
-                        to_currency=to_currency,
-                        rate=rate,
-                        date=timezone.now(),
-                    )
+                    if service.singleton:
+                        # Try to get the last automatically created exchange rate
+                        exchange_rate = (
+                            ExchangeRate.objects.filter(
+                                automatic=True,
+                                from_currency=from_currency,
+                                to_currency=to_currency,
+                            )
+                            .order_by("-date")
+                            .first()
+                        )
+                    else:
+                        exchange_rate = None
+
+                    if not exchange_rate:
+                        ExchangeRate.objects.create(
+                            automatic=True,
+                            from_currency=from_currency,
+                            to_currency=to_currency,
+                            rate=rate,
+                            date=timezone.now(),
+                        )
+                    else:
+                        exchange_rate.rate = rate
+                        exchange_rate.date = timezone.now()
+                        exchange_rate.save()
+
                     processed_pairs.add((from_currency.id, to_currency.id))
 
             service.last_fetch = timezone.now()

app/apps/currencies/forms.py

@@ -114,6 +114,7 @@ class ExchangeRateServiceForm(forms.ModelForm):
             "fetch_interval",
             "target_currencies",
             "target_accounts",
+            "singleton",
         ]
 
     def __init__(self, *args, **kwargs):
@@ -126,6 +127,7 @@ class ExchangeRateServiceForm(forms.ModelForm):
             "name",
             "service_type",
             Switch("is_active"),
+            Switch("singleton"),
             "api_key",
             Row(
                 Column("interval_type", css_class="form-group col-md-6"),

app/apps/currencies/migrations/0015_exchangerate_automatic_exchangerateservice_singleton.py

@@ -0,0 +1,23 @@
+# Generated by Django 5.2.4 on 2025-08-08 02:18
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('currencies', '0014_alter_currency_options'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='exchangerate',
+            name='automatic',
+            field=models.BooleanField(default=False, verbose_name='Automatic'),
+        ),
+        migrations.AddField(
+            model_name='exchangerateservice',
+            name='singleton',
+            field=models.BooleanField(default=False, help_text='Create one exchange rate and keep updating it. Avoids database clutter.', verbose_name='Single exchange rate'),
+        ),
+    ]

app/apps/currencies/models.py

@@ -70,6 +70,8 @@ class ExchangeRate(models.Model):
     )
     date = models.DateTimeField(verbose_name=_("Date and Time"))
 
+    automatic = models.BooleanField(verbose_name=_("Automatic"), default=False)
+
     class Meta:
         verbose_name = _("Exchange Rate")
         verbose_name_plural = _("Exchange Rates")
@@ -148,6 +150,14 @@ class ExchangeRateService(models.Model):
         blank=True,
     )
 
+    singleton = models.BooleanField(
+        verbose_name=_("Single exchange rate"),
+        default=False,
+        help_text=_(
+            "Create one exchange rate and keep updating it. Avoids database clutter."
+        ),
+    )
+
     class Meta:
         verbose_name = _("Exchange Rate Service")
         verbose_name_plural = _("Exchange Rate Services")