Re: [Django] #35976: Document Options.original_attrs (was: Persist original Meta class on Options instances)

[Django]

#35976: Document Options.original_attrs
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Reporter: Tim McCurrach | Owner: (none)
Type: Uncategorized | Status: new
Component: Documentation | Version: 5.1
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0
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Changes (by Tim McCurrach):

* summary: Persist original Meta class on Options instances => Document
Options.original_attrs


Old description:

> When a `model.Model` class is created
> [https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L112
> the metaclass `pop`s off] any `Meta` attribue defined on the model
> [https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L122
> before calling] `super.__new__()`. We do
> [https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L145
> pass it as an argument] to the `Options` class, and
> [https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/options.py#L136
> it's stored] on the `Options` instance, however
> [https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/options.py#L232
> this is then deleted] whilst the `Options.contribute_to_class` class is
> called. The attributes from the meta value are stored on a
> `original_attrs` attribute however. It might be a good idea to document
> this!!
>
> === Motivation for the documentation ===
>
> The motivation for this came change is born out of a desire to write a
> check that `db_table` is explicitly defined on all my models (even if it
> matches the default value that django would apply). I can write checks
> that require things like `ordering` is defined (or not defined) on a
> model. The problem with `db_table` is that defaults are applied when
> `contribute_to_class` is called. This means we need a reference to the
> underlying original Meta data. The `original_attrs` attribute is perfect
> for this, but as far as I can tell it isn't documented anywhere.

New description:

When a `model.Model` class is created
[https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L112
the metaclass `pop`s off] any `Meta` attribue defined on the model
[https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L122
before calling] `super.__new__()`. We do
[https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/base.py#L145
pass it as an argument] to the `Options` class, and
[https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/options.py#L136
it's stored] on the `Options` instance, however
[https://github.com/django/django/blob/ded485464214a3f69b64402b7d82221279f80008/django/db/models/options.py#L232
this is then deleted] whilst the `Options.contribute_to_class` class is
called. The attributes from the meta value are stored on a
`original_attrs` attribute however. It might be a good idea to document
that this attribute exists.

=== Motivation for the documentation ===

The motivation for this came change is born out of a desire to write a
check that `db_table` is explicitly defined on all my models (even if it
matches the default value that django would apply). I can write checks
that require things like `ordering` is defined (or not defined) on a
model. The problem with `db_table` is that defaults are applied when
`contribute_to_class` is called. This means we need a reference to the
underlying original Meta data. The `original_attrs` attribute is perfect
for this, but as far as I can tell it isn't documented anywhere.

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Ticket URL: <https://code.djangoproject.com/ticket/35976#comment:5>
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