get_manager short ut function proposal

[Ramez Ashraf]

Hello everyone, 

I want to propose a helper function
`get_manager(parent_manager=None, *args, **kwargs)` 

A shortcut to return a manager, *args & **kwargs are passed to the manager .filter()
pass parent_manager to customize the parent manager, defaults to ``Manager``.

it can be used like this 

from django.db.models import get_manager

class Person(models.Model):
    # ...
    authors = models.get_manager(role='A')
    editors = models.get_manager(role='E')
    special = get_manager(~Q(name="Roald Dahl"), role='E')
    manager_with_counts = get_manager(parent_manager=PollManager, name="Roald Dahl")

Instead of the current 

class AuthorManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(role='A')

class EditorManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(role='E')

class Person(models.Model):
    people = models.Manager()
    authors = AuthorManager()
    editors = EditorManager()

   ...

The first is more readable and nicer .. yeah ?
Code is working and ready at  github ,  

Do i get +1(s) to move forward and create a ticket ? 

[Adam Johnson]

Your proposal is quite niche: it only shortens the creation of a Manager class when you need to add a single filter() call. The function seems like it might be a useful helper within a project, if you use many such managers. But custom managers might use any queryset methods, or other logic. I've often used a custom manager to add annotate() and prefetch_related() calls.

So, I think your shortcut is a smart addition for your project, but perhaps not suitable for Django itself. I think it's worth sharing in a blog post though!

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[Ramez Ashraf]

Hello Adam 

Happy new year!

Thank you for the feedback, really appreciate it.

I thought the same like you at first, a cool function in my project (which is indeed the case)

One thing that gave me more incentive is the documentation code example.

IMO, i can see how shorter (and more readable) it would be with the proposed shortcut.

In fact it's indeed simple and doesn't offer the full support a real declared custom manager class would do. It's intended to be something like get_object_or_404.

Interested or do you think the function can be enhanced it to make more useable for your everyday other cases ?

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[Shai Berger]

On Sun, 1 Jan 2023 16:33:45 +0200
Ramez Ashraf <ramez...@gmail.com> wrote:

>
> Interested or do you think the function can be enhanced it to make
> more useable for your everyday other cases ?
>

This is half-baked, just a thought, but maybe you can take it some
place interesting:

Imagine a class that "collects" calls for later execution. Something
like (this exactly won't work, details below):

from functools import partialmethod
from django.db.models import QuerySet as QSet

class QS:
def __init__(self):
self._calls = []
def filter(self, *args, **kw):
self._calls.append(
partialmethod(QSet.filter, *args, **kw)
)
return self
def annotate(*args, **kw):
# ... (same idea)
# ... other relevant methods,
def __call__(self, qset):
for call in self._calls:
qset = apply(call, qset)
return qset

This won't work, I think, because partialmethod isn't supposed to work
quite this way, and the "apply" in the last line isn't defined. But
with this (fixed) already you could, I think, do something like

def qset_manager(qs: QS) -> Manager
class CustomManager(models.Manager):
def get_queryset(self):
orig = super().get_queryset()
return qs(orig)
return CustomManager()

And then, in your model,

class Person(models.Model):
...
authors = qset_manager(QS().filter(role="A"))

and now the "make a manager with a modified queryset" pattern is
shortened in a general way.

As I said, just a half-baked thought. There's problems here to solve,
and many improvements to make.

HTH,
Shai.

[Ramez Ashraf]

Mmmm I believe what you shared Shai is very sophisticated than what is proposed.

The proposal is a shortcut function for with ability to have a custom parent for more usability for an everyday use , like what's in the documentation about managers.

My proposal is *not* a new way to write managers . This can be your or someone else's fully baked idea.

With respect.