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

Brian Bouterse bmbouter at redhat.com
Wed Aug 7 21:15:14 UTC 2019 

On Wed, Aug 7, 2019 at 3:05 PM David Davis <daviddavis at redhat.com> wrote:

> 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.
>
+1 to doing both. Thank you for bringing this up.


> 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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