pre_delete and post_delete signals in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the pre_delete signal in Django?

The pre_delete signal is sent just before a model instance is deleted. It allows you to run custom code or cleanup tasks before the actual deletion happens.

beginner

When is the post_delete signal triggered in Django?

The post_delete signal is triggered immediately after a model instance has been deleted from the database. It is useful for actions that should happen after deletion, like clearing caches or logging.

intermediate

How do you connect a function to the pre_delete signal for a model?

You use the @receiver(pre_delete, sender=YourModel) decorator above your function or call pre_delete.connect(your_function, sender=YourModel). This tells Django to run your function before deleting instances of that model.

intermediate

Can you stop the deletion of an object inside a pre_delete signal handler?

No, the pre_delete signal does not support stopping the deletion. It is only for running code before deletion. To prevent deletion, you should override the model's delete() method or use database constraints.

beginner

Give an example use case for the post_delete signal.

A common use case is deleting related files from the file system after a model instance with a file field is deleted. The post_delete signal lets you remove those files safely after the database record is gone.

Which signal runs before a Django model instance is deleted?

A post_delete

B pre_delete

C pre_save

D post_save

The pre_delete signal is sent just before the deletion of a model instance.

What can you do inside a post_delete signal handler?

A Run code after the instance is deleted

B Modify the instance before deletion

C Prevent the deletion

D Cancel the deletion process

post_delete runs after deletion, so you can run cleanup or logging code then.

How do you connect a function to a Django signal?

A By calling the signal directly in templates

B By overriding the model's save() method

C Using @receiver decorator or connect() method

D By importing the signal in views.py

You connect signal handlers using the @receiver decorator or the connect() method.

Can pre_delete signal stop the deletion of an object?

A No, it only runs before deletion

B Yes, by raising an exception

C Yes, by returning False

D Yes, by calling cancel()

pre_delete cannot stop deletion; it only allows running code before deletion.

Which of these is a good use for post_delete?

A Preventing deletion of an object

B Validating data before saving

C Modifying data before saving

D Deleting related files after record deletion

post_delete is ideal for cleanup tasks like deleting files after the database record is removed.

Explain the difference between pre_delete and post_delete signals in Django.

Think about when each signal is triggered relative to the deletion event.

Describe how to connect a function to the pre_delete signal for a Django model and what you might use it for.

Focus on the connection method and practical uses.