GSOC 2023 Discussion and Feedback: Database-level Cascades

[Akash Sen]

Hello everyone,
I’ve started this discussion to get feedback for my proposal for the 
project: Database-level Cascades Functionality to Django ORM. I have never 
contributed to any of the official Django projects earlier but I have 
experience using the framework for last 2 years. In this discussion I would 
like to propose a high level view of how this can be implemented, any kind 
of feedback and reference to resources for a more detailed and clear 
perspective about the project from your side would be very much appreciated,

Based on my study it seems quite straightforward and simple to implement.

   1. Conduct thorough research and gain an understanding of the existing 
   discussions, pull requests, and issues associated with adding support for 
   database-level cascading options in the Django web framework.
   2. Specify the requirements for the new feature, including its name and 
   behavior, and determine whether it should be a new option (on_delete_db) or 
   a modification of the existing one (on_delete).
   3. Develop a ForeignKey subclass that sets a flag indicating that the 
   database should manage the cascading options.
   4. Modify the DatabaseSchemaEditor’s add_field() and sql_create_fk() 
   methods to recognize the flag and generate SQL accordingly for the specific 
   database backend.
   5. Ensure that the implementation performs as intended when tested for a 
   single database backend. Then, generalize the implementation so that it 
   works for all supported database backends, generating appropriate SQL for 
   each.
   6. Integrate the implementation with the Django migrations framework to 
   ensure proper handling of database-level cascading options during schema 
   migrations.
   7. Write tests to verify that the new feature functions correctly and 
   does not interfere with existing functionality.
   8. Submit one or more pull requests containing the changes, and 
   collaborate with the Django community to address any feedback or issues 
   that may arise.

Here is a link to my proposal : Database-level Cascades Proposal - GSoC '23 
- Google Docs 5 


Due to my beginner level understanding of the codebase there is a lot of 
scope room for improvement. Your suggestions will be of great help.

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Re: GSOC 2023 Discussion and Feedback: Database-level Cascades

[David Sanders]

Hi Akash,

Database-level cascading deletes is a topic that has been discussed often
since, well probably the dawn of Django 😁  From recollection the main
issue isn't the implementation, it's getting it to play nicely with
Django's cascading emulation.

There are other tickets, but I believe this is the main ticket to refer to:
https://code.djangoproject.com/ticket/21961  There are also plenty of
threads on this group I'm sure you could dig up.

Note that with the introduction of constraints a while back, there's
nothing stopping people from adding their own custom foreign keys that adds
the necessary `ON DELETE` clauses. Here's a demonstration of that:
https://github.com/shangxiao/stupid-django-tricks/tree/master/abusing_constraints#database-level-cascading-deletes

The gist is:

   1. Set your fks to "do nothing" (I haven't tested with other options -
   seems like there could be some conflicts there though)
   2. Define your own fk by extending BaseConstraint and add the necessary
   ON DELETE/ON UPDATE clauses
   3. Add this new fk to your meta's constraints attribute

Check out the tests in that link above for confirmation (only tested on
Postgres).

Anyway, best of luck!
David


On Tue, 28 Mar 2023 at 00:57, Akash Sen  wrote:

> Hello everyone,
> I’ve started this discussion to get feedback for my proposal for the
> project: Database-level Cascades Functionality to Django ORM. I have never
> contributed to any of the official Django projects earlier but I have
> experience using the framework for last 2 years. In this discussion I would
> like to propose a high level view of how this can be implemented, any kind
> of feedback and reference to resources for a more detailed and clear
> perspective about the project from your side would be very much appreciated,
>
> Based on my study it seems quite straightforward and simple to implement.
>
>1. Conduct thorough research and gain an understanding of the existing
>discussions, pull requests, and issues associated with adding support for
>database-level cascading options in the Django web framework.
>2. Specify the requirements for the new feature, including its name
>and behavior, and determine whether it should be a new option
>(on_delete_db) or a modification of the existing one (on_delete).
>3. Develop a ForeignKey subclass that sets a flag indicating that the
>database should manage the cascading options.
>4. Modify the DatabaseSchemaEditor’s add_field() and sql_create_fk()
>methods to recognize the flag and generate SQL accordingly for the specific
>database backend.
>5. Ensure that the implementation performs as intended when tested for
>a single database backend. Then, generalize the implementation so that it
>works for all supported database backends, generating appropriate SQL for
>each.
>6. Integrate the implementation with the Django migrations framework
>to ensure proper handling of database-level cascading options during schema
>migrations.
>7. Write tests to verify that the new feature functions correctly and
>does not interfere with existing functionality.
>8. Submit one or more pull requests containing the changes, and
>collaborate with the Django community to address any feedback or issues
>that may arise.
>
> Here is a link to my proposal : Database-level Cascades Proposal - GSoC
> '23 - Google Docs 5
> 
>
> Due to my beginner level understanding of the codebase there is a lot of
> scope room for improvement. Your suggestions will be of great help.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django developers (Contributions to Django itself)" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to django-developers+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/django-developers/bd82a0de-8f0a-47b5-b40d-1672ed05736fn%40googlegroups.com
> 
> .
>

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