[add]: Loan repayment event

app/models/repayment.py

@@ -2,6 +2,7 @@ from datetime import datetime, timezone
 from app.extensions import db
 from app.models.customer import Customer
 from app.models.loan import Loan
+from sqlalchemy.exc import IntegrityError
 
 
 class Repayment(db.Model):
@@ -37,8 +38,13 @@ class Repayment(db.Model):
             product_id=product_id,
         )
 
-        db.session.add(repayment)
-        db.session.commit()
+        try:
+            db.session.add(repayment)
+            db.session.commit()
+        except IntegrityError as err:
+            db.session.rollback()
+            raise ValueError(f"Database integrity error: {err}")
+
         return repayment
 
     def __repr__(self):