[Pulp-dev] Master-detail inheritance in Pulp 3

Wed Aug 7 19:04:27 UTC 2019

So I've been working on the change to have plugin writers manually specify
default_related_name. In terms of pulpcore, I see two options:

1. Just document that this needs to be done
2. Enforce that default_related_name needs to be defined and raise an
exception if it is not.

I'd suggest we do both options 1 and 2. First of all, it's quite easy to
forget and overlook this detail in the docs. Raising an error could save a
plugin writer a lot of pain/grief later on. Secondly, there are a number of
plugins already and it's quite possible some plugin writers could miss this
email thread or the new documentation. Normally, I am all for giving plugin
writers freedom but this seems like one case we may want to try to enforce
a solution to prevent problems later on.

Thoughts?

David

On Fri, Aug 2, 2019 at 8:08 AM David Davis <daviddavis at redhat.com> wrote:

> Thanks for the feedback. It sounds like no one is opposed to having plugin
> writers specify default_related_name for Detail models so I plan to move
> forward with this solution next week if no one objects.
>
> David
>
>
> On Thu, Aug 1, 2019 at 4:39 AM Ina Panova <ipanova at redhat.com> wrote:
>
>> I am in favour of manually setting default_related_name and document this
>> in plugin writers guide.
>>
>>
>>
>> --------
>> Regards,
>>
>> Ina Panova
>> Senior Software Engineer| Pulp| Red Hat Inc.
>>
>> "Do not go where the path may lead,
>>  go instead where there is no path and leave a trail."
>>
>>
>> On Wed, Jul 24, 2019 at 7:06 PM David Davis <daviddavis at redhat.com>
>> wrote:
>>
>>> I think my main concern with the solution to remove model inheritance is
>>> that we either only apply it to the Content model and run the risk of
>>> having conflicts in other Master/Detail models (unlikely but possible). Or
>>> we apply it to all M/D models which is a huge undertaking (unless we can
>>> create some general solution?).
>>>
>>> David
>>>
>>>
>>> On Wed, Jul 24, 2019 at 10:09 AM Dana Walker <dawalker at redhat.com>
>>> wrote:
>>>
>>>> I like your solution using default_related_name [0] manually, as Brian
>>>> noted [1], it's more explicit and therefore more pythonic.
>>>>
>>>> That in mind, Daniel's alternative, not using model inheritance for the
>>>> Content models [2], while less simple a change initially, potentially had
>>>> significant performance gains and is also more explicit and pythonic.
>>>>
>>>> Should we still pursue this more complex fix for the improvements to
>>>> bulk_create since we'd rather have breaking changes early in development
>>>> than need to address them later?
>>>>
>>>> Or am I putting the cart before the horse by seeking optimization too
>>>> early?
>>>>
>>>> [0] https://pulp.plan.io/issues/4681#note-19
>>>> [1] https://pulp.plan.io/issues/4681#note-20
>>>> [2] https://pulp.plan.io/issues/4681#note-11
>>>>
>>>> Dana Walker
>>>>
>>>> She / Her / Hers
>>>>
>>>> Software Engineer, Pulp Project
>>>>
>>>> Red Hat <https://www.redhat.com>
>>>>
>>>> dawalker at redhat.com
>>>> <https://www.redhat.com>
>>>>
>>>>
>>>>
>>>> On Wed, Jul 24, 2019 at 8:24 AM David Davis <daviddavis at redhat.com>
>>>> wrote:
>>>>
>>>>> I want to bump this thread again. We've only had one person weigh in
>>>>> and this is a major change that'll affect all Pulp 3 plugins that we need
>>>>> to address soon. Please respond here or on the issue with feedback.
>>>>>
>>>>> David
>>>>>
>>>>>
>>>>> On Sun, Jul 21, 2019 at 10:49 AM Brian Bouterse <bbouters at redhat.com>
>>>>> wrote:
>>>>>
>>>>>> Thanks for the investigation and demo patch. I posted a +1 for the
>>>>>> manual option with reasoning here:
>>>>>> https://pulp.plan.io/issues/4681#note-20
>>>>>>
>>>>>> Other ideas and perspectives are welcome. I hope we can resolve this
>>>>>> issue soon as we approach RC4.
>>>>>>
>>>>>> On Wed, Jul 17, 2019 at 12:55 PM David Davis <daviddavis at redhat.com>
>>>>>> wrote:
>>>>>>
>>>>>>> I did some investigation and posted my findings[0]. Basically, it
>>>>>>> would be possible to solve this problem by defining default_related_name
>>>>>>> either manually or automatically on detail models. I don't know if we want
>>>>>>> to go this route so feedback is appreciated.
>>>>>>>
>>>>>>> [0] https://pulp.plan.io/issues/4681#note-19
>>>>>>>
>>>>>>> David
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Apr 29, 2019 at 2:16 PM David Davis <daviddavis at redhat.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> It seems like most people are in favor of setting the OneToOneField
>>>>>>>> or perhaps the default_related_name on the detail model. I think there’s
>>>>>>>> also some interest in seeing how we can do this automatically for plugins.
>>>>>>>> I’ve added this feedback to the issue:
>>>>>>>>
>>>>>>>> https://pulp.plan.io/issues/4681#note-8
>>>>>>>>
>>>>>>>> David
>>>>>>>>
>>>>>>>>
>>>>>>>> On Wed, Apr 24, 2019 at 6:22 AM Ina Panova <ipanova at redhat.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> I would avoid making changes in class naming. So +1 for the
>>>>>>>>> OneToOneField definition.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --------
>>>>>>>>> Regards,
>>>>>>>>>
>>>>>>>>> Ina Panova
>>>>>>>>> Software Engineer| Pulp| Red Hat Inc.
>>>>>>>>>
>>>>>>>>> "Do not go where the path may lead,
>>>>>>>>>  go instead where there is no path and leave a trail."
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Apr 23, 2019 at 6:45 PM David Davis <daviddavis at redhat.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> The default_related_name setting is something that django
>>>>>>>>>> provides. Subclasses can also explicitly define their OneToOneField parent
>>>>>>>>>> link as well:
>>>>>>>>>>
>>>>>>>>>> content_ptr = models.OneToOneField(Content,
>>>>>>>>>> on_delete=models.CASCADE, parent_link=True, related_name='rpm_package')
>>>>>>>>>>
>>>>>>>>>> I am not sure what you mean by 'robust' but if a plugin subclass
>>>>>>>>>> doesn't do either of these, it may not work with other plugins.
>>>>>>>>>>
>>>>>>>>>> I think the question now would be whether we should just document
>>>>>>>>>> this or try to do it automagically for plugins?
>>>>>>>>>>
>>>>>>>>>> David
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, Apr 23, 2019 at 12:31 PM Brian Bouterse <
>>>>>>>>>> bbouters at redhat.com> wrote:
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Tue, Apr 23, 2019 at 11:02 AM David Davis <
>>>>>>>>>>> daviddavis at redhat.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> I think I found another solution that might work best: defining
>>>>>>>>>>>> 'default_related_name' on subclassed master-detail models. So Package in
>>>>>>>>>>>> pulp_rpm would define its default_related_name as "rpm_package".
>>>>>>>>>>>>
>>>>>>>>>>> Would we be making 'default_related_name' or is that something
>>>>>>>>>>> Django is providing? If it's something Pulp would be providing perhaps
>>>>>>>>>>> defining the explicit one-to-one field is better. Any plugin that takes the
>>>>>>>>>>> step of defining the one-to-one field will insulate themselves from other
>>>>>>>>>>> plugins. If plugins don't take that step they will still work, just not as
>>>>>>>>>>> robustly. Am I thinking about this correctly?
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> David
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Apr 23, 2019 at 10:29 AM David Davis <
>>>>>>>>>>>> daviddavis at redhat.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> I wanted to email the pulp-dev list about a major problem[0]
>>>>>>>>>>>>> that was recently encountered in Pulp 3 that affects how the Pulp 3 plugin
>>>>>>>>>>>>> API functions.
>>>>>>>>>>>>>
>>>>>>>>>>>>> # Problem
>>>>>>>>>>>>>
>>>>>>>>>>>>> In the plugin API we rely on inheritance to allow plugin
>>>>>>>>>>>>> writers to import functionality into their plugin. This includes models
>>>>>>>>>>>>> such as Remote and Content that are inherited by plugins. We rely on
>>>>>>>>>>>>> django's multi-table inheritance[1] for these models.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Behind the scenes, django defines a OneToOneField and a
>>>>>>>>>>>>> reverse accessor. This field is not namespace so if two subclasses have the
>>>>>>>>>>>>> same name, you get an error ("Reverse accessor for 'Package.content_ptr'
>>>>>>>>>>>>> clashes with reverse accessor for 'Package.content_ptr'.")
>>>>>>>>>>>>>
>>>>>>>>>>>>> To give an actual example, both the Debian and RPM plugins
>>>>>>>>>>>>> implement a Package class. This causes an error to be raised when a user
>>>>>>>>>>>>> installs both plugins. Django tries to define a 'package' reverse accessor
>>>>>>>>>>>>> for both subclasses and blows up.
>>>>>>>>>>>>>
>>>>>>>>>>>>> # Potential Solutions
>>>>>>>>>>>>>
>>>>>>>>>>>>> ## Class Naming
>>>>>>>>>>>>>
>>>>>>>>>>>>> The first solution I can think of which is probably also the
>>>>>>>>>>>>> simplest and most straightforward would be to require plugin writers to
>>>>>>>>>>>>> namespace their master/detail subclass names. So Package would be
>>>>>>>>>>>>> RpmPackage. This places the onus on plugin writers to name their
>>>>>>>>>>>>> master/detail classes correctly.
>>>>>>>>>>>>>
>>>>>>>>>>>>> ## Defining OneToOneField
>>>>>>>>>>>>>
>>>>>>>>>>>>> The other solution would be to either manually define the
>>>>>>>>>>>>> OneToOneField on the subclasses[2] and specify a namespaced field name.
>>>>>>>>>>>>> There may be a way to do this dynamically (ie magically) in the parent
>>>>>>>>>>>>> somehow as well.
>>>>>>>>>>>>>
>>>>>>>>>>>>> ## Abstract Class
>>>>>>>>>>>>>
>>>>>>>>>>>>> Lastly, we could redefine master models as abstract
>>>>>>>>>>>>> classes[3]. I can think of at least one or two places (e.g. content field
>>>>>>>>>>>>> on RepositoryVersionContent, publisher field on Publication) that would
>>>>>>>>>>>>> have to switch their relationships to generic relationships in order to
>>>>>>>>>>>>> accommodate this change.
>>>>>>>>>>>>>
>>>>>>>>>>>>> There might be other solutions I am not thinking of so feel
>>>>>>>>>>>>> free to propose something. Also, quick feedback would be greatly
>>>>>>>>>>>>> appreciated as this is going to be a major change in our plugin API.
>>>>>>>>>>>>>
>>>>>>>>>>>>> [0] https://pulp.plan.io/issues/4681
>>>>>>>>>>>>> [1]
>>>>>>>>>>>>> https://docs.djangoproject.com/en/2.2/topics/db/models/#multi-table-inheritance
>>>>>>>>>>>>> [2]
>>>>>>>>>>>>> https://docs.djangoproject.com/en/2.2/topics/db/models/#specifying-the-parent-link-field
>>>>>>>>>>>>> [3]
>>>>>>>>>>>>> https://docs.djangoproject.com/en/2.2/topics/db/models/#abstract-base-classes
>>>>>>>>>>>>>
>>>>>>>>>>>>> David
>>>>>>>>>>>>>
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> Pulp-dev mailing list
>>>>>>>>>>>> Pulp-dev at redhat.com
>>>>>>>>>>>> https://www.redhat.com/mailman/listinfo/pulp-dev
>>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>> Pulp-dev mailing list
>>>>>>>>>> Pulp-dev at redhat.com
>>>>>>>>>> https://www.redhat.com/mailman/listinfo/pulp-dev
>>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>> Pulp-dev mailing list
>>>>> Pulp-dev at redhat.com
>>>>> https://www.redhat.com/mailman/listinfo/pulp-dev
>>>>>
>>>> _______________________________________________
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>>
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