[add]: balance when calculating loan total

app/models/loan.py

@@ -30,6 +30,7 @@ class Loan(db.Model):
     continuous_fee = db.Column(db.Float, default=0)
     upfront_fee = db.Column(db.Float, nullable=True, default=0.0)
     repayment_amount = db.Column(db.Float, nullable=True, default=0.0)
+    balance = db.Column(db.Float, nullable=True, default=0.0)
     installment_amount = db.Column(db.Float, nullable=True, default=0.0)
     status = db.Column(db.String(20), default='pending')
     tenor = db.Column(db.Integer, nullable=True)
@@ -230,10 +231,10 @@ class Loan(db.Model):
             raise ValueError(f"Customer with Id {customer_id} does not have any loan.")
 
         total_amount = (
-            db.session.query(func.coalesce(func.sum(cls.current_loan_amount), 0.0))
+            cls.query.with_entities(func.coalesce(func.sum(cls.balance), 0.0))
             .filter_by(customer_id=customer_id)
             .scalar()
-        )    
+        )
 
         logger.info(f"Found {len(customer_loans)} loans for customer ID: {customer_id} with total amount: {total_amount}")