[update]: model class methods

app/models/loan.py

@@ -15,5 +15,18 @@ class Loan(db.Model):
     created_at = db.Column(db.DateTime, default=datetime.utcnow)
     updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
 
+
+    @classmethod
+    def has_active_loans(cls, customer_id):
+        active_loans = cls.query.filter_by(
+            customer_id=customer_id,
+            status='active'
+        ).count()
+
+        if active_loans > 0:
+            return False, "Customer has active loans"
+        return True, "No active loans"
+    
+    
     def __repr__(self):
         return f'<Loan {self.id}>'