Database transaction code adapted for more safety

app.py

@@ -76,41 +76,53 @@ def db_to_json():
 
 def json_to_db(data):
     try:
+        # Start a single transaction for all operations
+        with db.session.begin():
+            # Clear existing attendance records
             db.session.query(Attendance).delete()
-        db.session.commit()
             db.session.query(GuestName).delete()
-        db.session.commit()
-        db.session.query(Date).delete()
-        db.session.commit()
-        db.session.query(Player).delete()
-        db.session.commit()
-    except Exception as e:
-        db.session.rollback()
-        print("Error during deletion:", e)
-        raise
             
-    # Insert players from JSON
+            # Update players - keep existing ones, add new ones
+            existing_players = {p.name: p for p in Player.query.all()}
             for name in data.get("players", []):
+                if name not in existing_players:
                     db.session.add(Player(name=name))
-    db.session.commit()
             
-    # Insert dates and attendance
+            # Update dates - keep existing ones, add new ones
+            existing_dates = {d.date_str: d for d in Date.query.all()}
             for date_str in data.get("dates", []):
+                if date_str not in existing_dates:
                     date = Date(date_str=date_str)
                     db.session.add(date)
-        db.session.commit()
+                    existing_dates[date_str] = date
+            
+            # Refresh player list after potential additions
+            player_dict = {p.name: p for p in Player.query.all()}
+            
+            # Add attendance records
+            for date_str in data.get("dates", []):
+                date = existing_dates[date_str]
                 for idx, player_name in enumerate(data["players"] + [data["guest"]]):
                     key = f"{date_str}|{idx}"
                     status = data["attendance"].get(key)
-            if status:
+                    if status and player_name in player_dict:
-                player = Player.query.filter_by(name=player_name).first()
+                        player = player_dict[player_name]
-                if player:
+                        # Convert boolean True to string 'yes'
-                    # Save status as 'yes', 'no', or 'maybe'
+                        status_value = 'yes' if status is True else status
-                    db.session.add(Attendance(date_id=date.id, player_id=player.id, status='yes' if status is True else status if status in ['no', 'maybe'] else None))
+                        # Only add if status is one of the valid values
+                        if status_value in ['yes', 'no', 'maybe']:
+                            db.session.add(Attendance(date_id=date.id, player_id=player.id, status=status_value))
+                
+                # Add guest name if present
                 guest_name = data.get("guestNames", {}).get(date_str)
                 if guest_name:
                     db.session.add(GuestName(date_id=date.id, name=guest_name))
-    db.session.commit()
+            
+            # The transaction will be committed automatically if no exceptions occur
+    except Exception as e:
+        # The transaction will be rolled back automatically if an exception occurs
+        print("Error during database operation:", e)
+        raise