LingoRecentTransactionsCell: optimize query (#68212)

- use an union instead of an OR
- use the fact that union is an implicit distinct to simplify the code
- index the start_date field so it can be used to filter efficiently

combo/apps/lingo/migrations/0047_transaction_index_startdate.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('lingo', '0046_display_condition'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='Transaction',
+            name='start_date',
+            field=models.DateTimeField(auto_now_add=True, db_index=True),
+        ),
+    ]

combo/apps/lingo/models.py

@@ -815,7 +815,7 @@ class Transaction(models.Model):
     items = models.ManyToManyField(BasketItem, blank=True)
     remote_items = models.CharField(max_length=512)
     to_be_paid_remote_items = models.CharField(max_length=512, null=True)
-    start_date = models.DateTimeField(auto_now_add=True)
+    start_date = models.DateTimeField(auto_now_add=True, db_index=True)
     end_date = models.DateTimeField(null=True)
     bank_data = JSONField(blank=True, default=dict)
     order_id = models.CharField(max_length=200)
@@ -1110,9 +1110,10 @@ class LingoRecentTransactionsCell(CellBase):
         # list transactions :
         # * paid by the user
         # * or linked to a BasketItem of the user
-        qs = Transaction.objects.filter(models.Q(user=user) | models.Q(items__user=user)).filter(
+        qs_recent_txn = Transaction.objects.filter(
             start_date__gte=timezone.now() - datetime.timedelta(days=7)
         )
+        qs = qs_recent_txn.filter(user=user).union(qs_recent_txn.filter(items__user=user))
         if poll:
             for transaction in qs:
                 if transaction.can_poll_backend() and transaction.is_running():
@@ -1128,9 +1129,7 @@ class LingoRecentTransactionsCell(CellBase):
 
     def render(self, context):
         recent_transactions_template = template.loader.get_template('lingo/combo/recent_transactions.html')
-        context['transactions'] = (
-            self.get_transactions_queryset(context, poll=True).distinct().order_by('-start_date')
-        )
+        context['transactions'] = self.get_transactions_queryset(context, poll=True).order_by('-start_date')
         return recent_transactions_template.render(context)