Django RecursionError in from_db() Method

The RecursionError you're encountering is caused by overriding the __init__ method in your Erfasst model while trying to access attributes that don't exist yet during the model loading process.

The Problem

When Django loads model instances from the database using from_db(), it creates the instance and then sets up its state. Your custom __init__ method is trying to access self.status_id and self.approved_at before they're properly initialized when the model is being loaded from the database.

This creates an infinite recursion because:

1. from_db() tries to create an instance using cls(*values)
2. Your __init__ method tries to access self.status_id
3. This triggers attribute access before the model is fully initialized
4. This leads to another call to initialize attributes
5. Which again calls your __init__ method, and so on

The Solution

According to Django's documentation, you should avoid overriding __init__ for this exact reason. Instead, there are two better approaches:

Option 1: Use from_db() to track original values

PYTHONCopied
class Erfasst(models.Model):
    status = models.ForeignKey(Status, models.PROTECT)
    approved_at = models.DateTimeField(null=True, blank=True)
    
    @classmethod
    def from_db(cls, db, field_names, values):
        instance = super().from_db(db, field_names, values)
        # Store original values after the instance is properly loaded
        instance._old_status_id = instance.status_id
        instance._old_approved_at = instance.approved_at
        return instance

Option 2: Use a post_init signal

PYTHONCopied
from django.db import models
from django.db.models.signals import post_init

class Erfasst(models.Model):
    status = models.ForeignKey(Status, models.PROTECT)
    approved_at = models.DateTimeField(null=True, blank=True)

def store_original_values(sender, instance, **kwargs):
    instance._old_status_id = instance.status_id
    instance._old_approved_at = instance.approved_at

post_init.connect(store_original_values, sender=Erfasst)

Important Note on Transactions

Remember that Django doesn't automatically revert model field values when a transaction is rolled back. If you're using these original values to detect changes and make decisions, you might need to manually restore field values in case of transaction failures, as shown in the documentation:

PYTHONCopied
from django.db import DatabaseError, transaction

obj = Erfasst(...)
original_status_id = obj.status_id
obj.status_id = new_status_id
try:
    with transaction.atomic():
        obj.save()
except DatabaseError:
    obj.status_id = original_status_id

By implementing one of these solutions, you should be able to resolve the RecursionError while still maintaining the ability to track original field values.