add loan and loan_charges model

app/models/loan_charge.py

@@ -0,0 +1,43 @@
+from datetime import datetime, timezone, timedelta
+from app.extensions import db
+from sqlalchemy.orm import relationship
+
+class LoanCharge(db.Model):
+    __tablename__ = 'loan_charges'
+
+    id = db.Column(db.Integer, primary_key=True, autoincrement=True)
+    loan_id = db.Column(db.Integer, nullable=False)
+    transaction_id = db.Column(db.String(50), nullable=True)
+    code = db.Column(db.String(50), nullable=False)
+    amount = db.Column(db.Float, default=0.0)
+    percent = db.Column(db.Float, default=0.0)
+    description = db.Column(db.Text, nullable=True)
+    due = db.Column(db.Integer, nullable=False)
+    due_date = db.Column(db.DateTime, nullable=True)
+    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))
+
+    loan = relationship(
+        "Loan",
+        primaryjoin="LoanCharge.loan_id == Loan.id",
+        foreign_keys=[loan_id],
+        back_populates="loan_charges",
+    )
+
+    def __repr__(self):
+        return f"<LoanCharge {self.id} - Loan {self.loan_id} - {self.code}>"
+
+    def to_dict(self):
+        """
+        Convert the Loan charge object to a dictionary format for JSON serialization.
+        """
+        return {
+            'id': self.id,
+            'loanId': self.loan_id,
+            'transactionId': self.transaction_id,
+            'code': self.code,
+            'amount': self.amount,
+            'percent': self.percent,
+            'description': self.description,
+            'due': self.due
+        }