workx_backend/invoice/models.py

from django.db import models
from project.models import Project


class Invoice(models.Model):
    project = models.ForeignKey(Project)
    invoice_id = models.CharField(max_length=15)
    raised_date = models.DateField()
    due_date = models.DateField()
    is_paid = models.BooleanField()

    def __str__(self):
        return self.invoice_id