Borrowing-TrackerBackend/equipment_tracker/transactions/models.py

from django.db import models
from accounts.models import CustomUser
from equipments.models import EquipmentInstance
from django.utils.timezone import now
from django.core.cache import cache


class Transaction(models.Model):
    TRANSACTION_STATUS_CHOICES = (
        # Transaction is pending approval
        ('Pending Approval', 'Pending Approval'),
        # Transaction has been approved, pending delivery by labtech
        ('Approved', 'Approved'),
        # Tranasction has been rejected
        ('Rejected', 'Rejected'),
        # Transaction has been approved but has been cancelled due to rare circumstances
        ('Cancelled', 'Cancelled'),
        # Transaction has been delivered and is on borrow
        ('Borrowed', 'Borrowed'),
        # Transaction has been returned, pending checking
        ('Returned: Pending Checking', 'Returned: Pending Checking'),
        # Transaction has been breakages after being returned, pending resolution
        ('With Breakages: Pending Resolution',
            'With Breakages: Pending Resolution'),
        # Transaction has been finalized
        ('Finalized', 'Finalized'),
    )

    borrower = models.ForeignKey(
        CustomUser, on_delete=models.SET_NULL, null=True, related_name='borrowed_transactions')
    remarks = models.TextField(max_length=512, null=True)
    additional_members = models.TextField(max_length=512, null=True)
    consumables = models.TextField(max_length=512, null=True)
    teacher = models.ForeignKey(
        CustomUser, on_delete=models.SET_NULL, null=True, related_name='teacher_transactions')
    equipments = models.ManyToManyField(EquipmentInstance)
    transaction_status = models.CharField(
        max_length=40, choices=TRANSACTION_STATUS_CHOICES, default='Pending', db_index=True)
    subject = models.TextField(max_length=128)
    timestamp = models.DateTimeField(default=now, editable=False)

    def __str__(self):
        return f"Transaction #{self.id} under {self.teacher} by {self.borrower}"

    def save(self, *args, **kwargs):
        cache.delete('available_equipment_instances')
        cache.delete('equipment_instances')
        cache.delete('non_finalized_transactions')
        return super().save(*args, **kwargs)