Delegate exchange persistence to ExchangeRepository

- Add create() and update() methods to ExchangeRepository
- Update ExchangeService to use repository methods instead of direct db operations
- All persistence operations now go through repositories consistently
- Fix indentation errors in ExchangeService

backend/repositories/exchange.py

@@ -161,3 +161,32 @@ class ExchangeRepository:
             )
         )
         return {row[0] for row in result.all()}
+
+    async def create(self, exchange: Exchange) -> Exchange:
+        """
+        Create a new exchange record.
+
+        Args:
+            exchange: Exchange instance to persist
+
+        Returns:
+            Created Exchange record (committed and refreshed)
+        """
+        self.db.add(exchange)
+        await self.db.commit()
+        await self.db.refresh(exchange)
+        return exchange
+
+    async def update(self, exchange: Exchange) -> Exchange:
+        """
+        Update an existing exchange record.
+
+        Args:
+            exchange: Exchange instance to update
+
+        Returns:
+            Updated Exchange record (committed and refreshed)
+        """
+        await self.db.commit()
+        await self.db.refresh(exchange)
+        return exchange

backend/services/exchange.py

@@ -267,11 +267,8 @@ class ExchangeService:
             status=ExchangeStatus.BOOKED,
         )
 
-        self.db.add(exchange)
-
         try:
-            await self.db.commit()
-            await self.db.refresh(exchange)
+            return await self.exchange_repo.create(exchange)
         except IntegrityError as e:
             await self.db.rollback()
             # This should rarely happen now since we check explicitly above,
@@ -280,8 +277,6 @@ class ExchangeService:
                 "Database constraint violation. Please try again."
             ) from e
 
-        return exchange
-
     async def get_exchange_by_public_id(
         self, public_id: uuid.UUID, user: User | None = None
     ) -> Exchange:
@@ -331,10 +326,7 @@ class ExchangeService:
         )
         exchange.cancelled_at = datetime.now(UTC)
 
-        await self.db.commit()
-        await self.db.refresh(exchange)
-
-        return exchange
+        return await self.exchange_repo.update(exchange)
 
     async def complete_exchange(self, exchange: Exchange) -> Exchange:
         """
@@ -354,10 +346,7 @@ class ExchangeService:
         exchange.status = ExchangeStatus.COMPLETED
         exchange.completed_at = datetime.now(UTC)
 
-        await self.db.commit()
-        await self.db.refresh(exchange)
-
-        return exchange
+        return await self.exchange_repo.update(exchange)
 
     async def mark_no_show(self, exchange: Exchange) -> Exchange:
         """
@@ -379,10 +368,7 @@ class ExchangeService:
         exchange.status = ExchangeStatus.NO_SHOW
         exchange.completed_at = datetime.now(UTC)
 
-        await self.db.commit()
-        await self.db.refresh(exchange)
-
-        return exchange
+        return await self.exchange_repo.update(exchange)
 
     def _expand_availability_to_slots(
         self, avail: Availability, slot_date: date, booked_starts: set[datetime]