Model inheritance in different modules

[LBris]

Hi everyone,

Would it be possible to provide a new inheritance mechanism between classes 
in Django ?

I explain my point :

I have an app, for instance "HR": In this app, I would manage a model that 
is called "Employee". I store several information on this model and it's 
fine.

Suppose I have a SECOND app, for instance "Fleet". In this app, I would 
manage a model that is called "Vehicle" and of course I store several 
information on this model.

Suppose I only use the app "HR"  and one day, I decide to use the app 
"Fleet". That's okey, no problem. Both will work.

But what if I decide to create a THIRD app, for instance "HR-Fleet" that 
does the bridge between the two others ?

That means that HR can be used ALONE and same for Fleet.

But HR-Fleet would add additional information. For instance, on the 
employee we would add a field "company_car" that points to a vehicle. The 
trick is, it would be GREAT to be able to do that without creating 
additional table in the database.

Here is a sample of code to illustrate the behavior I'm trying to explain :

In app "HR" :

hr/employee.py :

class Employee(models.model):
   name = ...
   email = ...

In app "Fleet" :

fleet/vehicle.py

class Vehicle(models.model):
   brand = ...
   model = ...
   fuel_type = ...

In app "HR-Fleet" :

hr_fleet/employee.py :

class HRFleetEmployee(models.model):
   _inherit = 

   company_car = models.ForeignKey(...)


And that would add an extra field on the Employee model without adding any 
table in the database or using proxy model or ...

Can you guys tell me if that behavior is possible ?

If you don't get the point of such a functionnality, I can try to give more 
details or be more clear.

Thanks in advance.

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Re: Model inheritance in different modules

[Joe Tennies]

I think this is more of a django-users comment, so I'll post Adam's
template for places.

I think you've found the wrong mailing list for this post. This mailing
list is for the development of Django itself, not for support using Django.
This means the discussions of bugs and features in Django itself, rather
than in your code using it. People on this list are unlikely to answer your
support query with their limited time and energy. Read more on the mailing
lists at https://www.djangoproject.com/community/

For support, please use the NEW Django forum at
https://forum.djangoproject.com , django-users mailing list, or IRC #django
on Freenode, or a site like Stack Overflow. There are people out there
willing to help on those channels, but they might not respond if you don't
ask your question well. Stack Overflow's question guide can help you frame
it well: https://stackoverflow.com/help/how-to-ask .

Also if you haven't read it, please take a look at Django's Code of
Conduct: https://www.djangoproject.com/conduct/ . These are our "ground
rules" for working well as a community, and will help you get the most out
of Django and our fantastic community.

Thanks for your understanding,

Adam

I'll send you a direct message.

Joe


On Thu, Jan 30, 2020 at 6:02 AM LBris  wrote:

> Hi everyone,
>
> Would it be possible to provide a new inheritance mechanism between
> classes in Django ?
>
> I explain my point :
>
> I have an app, for instance "HR": In this app, I would manage a model that
> is called "Employee". I store several information on this model and it's
> fine.
>
> Suppose I have a SECOND app, for instance "Fleet". In this app, I would
> manage a model that is called "Vehicle" and of course I store several
> information on this model.
>
> Suppose I only use the app "HR"  and one day, I decide to use the app
> "Fleet". That's okey, no problem. Both will work.
>
> But what if I decide to create a THIRD app, for instance "HR-Fleet" that
> does the bridge between the two others ?
>
> That means that HR can be used ALONE and same for Fleet.
>
> But HR-Fleet would add additional information. For instance, on the
> employee we would add a field "company_car" that points to a vehicle. The
> trick is, it would be GREAT to be able to do that without creating
> additional table in the database.
>
> Here is a sample of code to illustrate the behavior I'm trying to explain :
>
> In app "HR" :
>
> hr/employee.py :
>
> class Employee(models.model):
>name = ...
>email = ...
>
> In app "Fleet" :
>
> fleet/vehicle.py
>
> class Vehicle(models.model):
>brand = ...
>model = ...
>fuel_type = ...
>
> In app "HR-Fleet" :
>
> hr_fleet/employee.py :
>
> class HRFleetEmployee(models.model):
>_inherit = 
>
>company_car = models.ForeignKey(...)
>
>
> And that would add an extra field on the Employee model without adding any
> table in the database or using proxy model or ...
>
> Can you guys tell me if that behavior is possible ?
>
> If you don't get the point of such a functionnality, I can try to give
> more details or be more clear.
>
> Thanks in advance.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django developers (Contributions to Django itself)" group.
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> email to django-developers+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/django-developers/7800872b-6191-4505-b3bb-f726b0b92db3%40googlegroups.com
> 
> .
>


-- 
Joe Tennies
tenn...@gmail.com

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CrossDB JSONField — Testing needed.

[Carlton Gibson]

Hi all. 

>From GSoC last year, Sage has a CrossDB JSONField for us: 

https://github.com/django/django/pull/12392

We still have a bit more close review to do but...


*We need people to give it an outing, to find issues/regressions and so 
on. *


 PostgreSQL:
Clone your DB etc. Change your Postgres JSONFields to the new 
`models.JSONField`, and so on. Create a migration. Migrate. Run your test 
suite. Did anything break? What wasn't clear from the docs?

 Other Databases: 
Do you have some JSON handy? Create a new JSONField model. Give it a run. 
What doesn't work? 


If you could allocate a bit of time to try this out it would be a real help 
to make sure the new field is somewhat battle tested before bringing it in. 

The PR there is a fresh one just for this purpose. :)

Thanks all. 

Kind Regards,

Carlton

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Re: Model inheritance in different modules

[LBris]

No this is not a django-user-code related post. The code I provided was 
only an example to illustrate the feature request.

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Re: Model inheritance in different modules

[Abhijeet Viswa]

How would the fields in HRFleetEmployee be persistent and linked to a
particular Employee or Vehicle without being saved in the database? Or did
I understand your code and request wrong?

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Re: Model inheritance in different modules

[LBris]

I've never said it isn't saved in database. It is saved but in the table of
the employee since hrfleetemployee inherits from employee. It simply adds
this field to the table of Employee

Le jeu. 30 janv. 2020 à 5:24 PM, Abhijeet Viswa  a
écrit :

> How would the fields in HRFleetEmployee be persistent and linked to a
> particular Employee or Vehicle without being saved in the database? Or did
> I understand your code and request wrong?
>
> --
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> 
> .
>

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Re: Model inheritance in different modules

[Abhijeet Viswa]

I think this would needlessly complicate the entire migration process. Two
different app migrations (and possibly even more) would have be considered
and executed in sequence to prevent anything breaking on the database.

On Thu, 30 Jan 2020 at 22:00, LBris  wrote:

> I've never said it isn't saved in database. It is saved but in the table
> of the employee since hrfleetemployee inherits from employee. It simply
> adds this field to the table of Employee
>
> Le jeu. 30 janv. 2020 à 5:24 PM, Abhijeet Viswa 
> a écrit :
>
>> How would the fields in HRFleetEmployee be persistent and linked to a
>> particular Employee or Vehicle without being saved in the database? Or did
>> I understand your code and request wrong?
>>
>> --
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>> email to django-developers+unsubscr...@googlegroups.com.
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>> 
>> .
>>
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> 
> .
>


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Abhijeet

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Re: Model inheritance in different modules

[LBris]

I do not understand. Could you explain to me what it would break the 
database and how ?

Le jeudi 30 janvier 2020 17:37:22 UTC+1, Abhijeet Viswa a écrit :
>
> I think this would needlessly complicate the entire migration process. Two 
> different app migrations (and possibly even more) would have be considered 
> and executed in sequence to prevent anything breaking on the database. 
>
> On Thu, 30 Jan 2020 at 22:00, LBris > 
> wrote:
>
>> I've never said it isn't saved in database. It is saved but in the table 
>> of the employee since hrfleetemployee inherits from employee. It simply 
>> adds this field to the table of Employee
>>
>> Le jeu. 30 janv. 2020 à 5:24 PM, Abhijeet Viswa > > a écrit :
>>
>>> How would the fields in HRFleetEmployee be persistent and linked to a 
>>> particular Employee or Vehicle without being saved in the database? Or did 
>>> I understand your code and request wrong? 
>>>
>>> -- 
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>>> Groups "Django developers (Contributions to Django itself)" group.
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>>>  
>>> 
>>> .
>>>
>> -- 
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>>  
>> 
>> .
>>
>
>
> -- 
> Abhijeet
>

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Re: Model inheritance in different modules

[Abhijeet Viswa]

Each model represents one table on the DB. Modifying it in two different
apps (hence creating two different sets of migrations) might result in
breaking changes. What if one migration affects something that is directly
referenced by the other app, but wasn't updated?

Also, what would the potential benefits be (other than reduction of number
of tables) to such a type of inheritance? Couldn't the same be done with
another table and a select related? The only difference would be a in
prefetch_related call (your inheritance wouldn't require one). However,
doing something that like that means the Employee app knows about (and
relies upon) this backward relation to the Vehicle model (and hence the 2nd
app itself).

On Thu, 30 Jan 2020 at 23:07, LBris  wrote:

> I do not understand. Could you explain to me what it would break the
> database and how ?
>
> Le jeudi 30 janvier 2020 17:37:22 UTC+1, Abhijeet Viswa a écrit :
>>
>> I think this would needlessly complicate the entire migration process.
>> Two different app migrations (and possibly even more) would have be
>> considered and executed in sequence to prevent anything breaking on the
>> database.
>>
>> On Thu, 30 Jan 2020 at 22:00, LBris  wrote:
>>
>>> I've never said it isn't saved in database. It is saved but in the table
>>> of the employee since hrfleetemployee inherits from employee. It simply
>>> adds this field to the table of Employee
>>>
>>> Le jeu. 30 janv. 2020 à 5:24 PM, Abhijeet Viswa  a
>>> écrit :
>>>
 How would the fields in HRFleetEmployee be persistent and linked to a
 particular Employee or Vehicle without being saved in the database? Or did
 I understand your code and request wrong?

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 .

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>>> 
>>> .
>>>
>>
>>
>> --
>> Abhijeet
>>
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> 
> .
>


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