eliminated some hardcoded values

app/models/customer.py

@@ -0,0 +1,41 @@
+from datetime import datetime, timezone
+from sqlalchemy.orm import relationship
+from app.extensions import db
+
+
+class Customer(db.Model):
+    __tablename__ = 'customers'
+
+    id = db.Column(db.String(50), primary_key=True)
+    msisdn = db.Column(db.String(20), unique=True, nullable=False)
+    country_code = db.Column(db.String(3), nullable=False)
+    created_at = db.Column(db.DateTime, default=datetime.now(timezone.utc))
+    updated_at = db.Column(db.DateTime, default=datetime.now(timezone.utc), onupdate=datetime.now(timezone.utc))
+
+    accounts = relationship(
+        "Account",
+        primaryjoin="Customer.id == Account.customer_id",
+        foreign_keys="Account.customer_id",
+        back_populates="customer",
+    )
+
+    loans = relationship(
+        "Loan",
+        primaryjoin="Customer.id == Loan.customer_id",
+        foreign_keys="Loan.customer_id",
+        back_populates="customer",
+    )
+
+    @classmethod
+    def get_customer(cls, customer_id):
+        """
+        Get customer by  ID.
+        """
+        customer = cls.query.filter_by(id=customer_id).first()
+
+        if not customer:
+            raise ValueError(f"Customer does not exist")
+        return customer
+
+    def __repr__(self):
+        return f'<Customer {self.id}>'