06/05 Optimize app

app/services/account_service.py

@@ -5,48 +5,45 @@ plus any incoming transfers minus outgoing transfers.
 """
 
 from decimal import Decimal
-from sqlalchemy import func
+from sqlalchemy import func, case, or_, and_
 from app.extensions import db
 from app.models.account import Account
 from app.models.transaction import Transaction
 
 
 def calc_balance(account_id):
-    """Recalculate and persist the balance for a given account."""
-    # Income credited to this account
-    income = db.session.query(
-        func.coalesce(func.sum(Transaction.amount), 0)
+    """
+    Recalculate and persist the balance for a given account.
+    Uses a single aggregation query with CASE expressions instead of 4 queries.
+    """
+    row = db.session.query(
+        func.coalesce(func.sum(case(
+            (and_(Transaction.account_id == account_id,
+                  Transaction.transaction_type == 'income'), Transaction.amount),
+            else_=0
+        )), 0),
+        func.coalesce(func.sum(case(
+            (and_(Transaction.account_id == account_id,
+                  Transaction.transaction_type == 'expense'), Transaction.amount),
+            else_=0
+        )), 0),
+        func.coalesce(func.sum(case(
+            (and_(Transaction.account_id == account_id,
+                  Transaction.transaction_type == 'transfer'), Transaction.amount),
+            else_=0
+        )), 0),
+        func.coalesce(func.sum(case(
+            (and_(Transaction.to_account_id == account_id,
+                  Transaction.transaction_type == 'transfer'), Transaction.amount),
+            else_=0
+        )), 0),
     ).filter(
-        Transaction.account_id == account_id,
-        Transaction.transaction_type == 'income'
-    ).scalar()
+        or_(Transaction.account_id == account_id,
+            Transaction.to_account_id == account_id)
+    ).one()
 
-    # Expenses debited from this account
-    expense = db.session.query(
-        func.coalesce(func.sum(Transaction.amount), 0)
-    ).filter(
-        Transaction.account_id == account_id,
-        Transaction.transaction_type == 'expense'
-    ).scalar()
-
-    # Transfers out (this account is source)
-    transfer_out = db.session.query(
-        func.coalesce(func.sum(Transaction.amount), 0)
-    ).filter(
-        Transaction.account_id == account_id,
-        Transaction.transaction_type == 'transfer'
-    ).scalar()
-
-    # Transfers in (this account is destination)
-    transfer_in = db.session.query(
-        func.coalesce(func.sum(Transaction.amount), 0)
-    ).filter(
-        Transaction.to_account_id == account_id,
-        Transaction.transaction_type == 'transfer'
-    ).scalar()
-
-    balance = Decimal(str(income)) - Decimal(str(expense)) \
-              - Decimal(str(transfer_out)) + Decimal(str(transfer_in))
+    income, expense, transfer_out, transfer_in = (Decimal(str(v)) for v in row)
+    balance = income - expense - transfer_out + transfer_in
 
     account = db.session.get(Account, account_id)
     if account: