[add]: Loan repayment event

app/models/loan.py

@@ -2,6 +2,7 @@ from datetime import datetime, timezone
 from app.extensions import db
 from app.models.customer import Customer
 from app.models.account import Account
+from sqlalchemy.exc import IntegrityError
 
 
 class Loan(db.Model):
@@ -44,8 +45,12 @@ class Loan(db.Model):
             status=status
         )
 
-        db.session.add(loan)
-        db.session.commit()
+        try:
+            db.session.add(loan)
+            db.session.commit()
+        except IntegrityError as err:
+            db.session.rollback()
+            raise ValueError(f"Database integrity error: {err}")
         return loan