Re: Managers, Queryset, inheritance and polymorphism

[Amirouche Boubekki]

Thx Lachlan, I'm not sure to understand everything, I think I will have to
track this variables in the code to see how they are used.

I found out about my bug, it was the import of a pyc that made all the
machinery buggy.

Thanks,

Amirouche

-- 
You received this message because you are subscribed to the Google Groups 
"Django users" group.
To post to this group, send email to django-users@googlegroups.com.
To unsubscribe from this group, send email to 
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at 
http://groups.google.com/group/django-users?hl=en.

Re: Managers, Queryset, inheritance and polymorphism

[Lachlan Musicman]

On Sat, Oct 6, 2012 at 3:14 AM, Amirouche  wrote:
> Héllo,
>
> I got a problem with manager, some of you may already know it, I try my best
> to like them, if anyone can explain me the purpose of their existence I will
> be so much grateful :)
>
> Like I said, I try my best but:
>
> 0) Documentation references «default_manager», but I don't find it in the
> code, is it a documentation bug ?

I don't think it's a bug, but I agree there is some mental gymnastics
that needs to happen. I remember the  same.

The default manager is usually the "objects" in MyModel.objects.all().

But if you add new managers, the TOP manager is the default manager -
as a result, a lot of people add the

objects = models.Manager()

to the top of their list of managers, followed by the self defined managers.

> 0bis) What is the purpose of «_default_manager» and «_base_manager» ?

Riffing from the top of my head, (ie, I don't know exact motivations,
but am pretty sure it's) that managers are integral to data use.

ie, the base_manager is the class in the code that gives us the
managers, and the default manager is the standard out of the box
manager. Base exists so that managers can be extended.

Look at your code. How often do you use MyModel.objects.all() or
MyModel.objects.filter(x=y) or anything like that at all? That's all
Managers. This is why we need managers - so that we don't have to
write SELECT * FROM TABLENAME WHERE X=Y (or whatever the SQL is)

I wish I could answer the rest of your questions, but I'm only new to
Django too :)
cheers
L.


> 1) What is the purpose of «Manager.db», it's not used in Manager class, so I
> don't think it's used anywhere else
>
> 2) Polymorphism
>
> Is there anyone that can debug two level and more of inheritance in
> Django-Polymorphic
> I think this a revision of Django Polymorphic that works with that problem,
> anyone knows the revision hash ?
> Do you know any other application that does polymorphism the way I need it
> (with several level of inheritance) ?
>
> If they are answers to question 2, I might no need the answer to the
> following questions, I still would like to know.
>
> I have the following models, manager and querysets
> https://gist.github.com/3826531
>
> According to the code of  Manager in manager.py, I just need to override
> «get_query_set», but here is what I get as results, the bug is in the second
> line:
>
>> In [14]: PolymorphicQuerySet(Entry)
>> Out[14]: [, , , ,
>> , , ]
>> In [15]: Entry.objects.all()
>> Out[15]: []
>
>
> What am I doing wrong ?
>
> Thanks,
>
>
> Amirouche
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django users" group.
> To view this discussion on the web visit
> https://groups.google.com/d/msg/django-users/-/G20heNLwu6IJ.
> To post to this group, send email to django-users@googlegroups.com.
> To unsubscribe from this group, send email to
> django-users+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/django-users?hl=en.



-- 
...we look at the present day through a rear-view mirror. This is
something Marshall McLuhan said back in the Sixties, when the world
was in the grip of authentic-seeming future narratives. He said, “We
look at the present through a rear-view mirror. We march backwards
into the future.”

http://www.warrenellis.com/?p=14314

-- 
You received this message because you are subscribed to the Google Groups 
"Django users" group.
To post to this group, send email to django-users@googlegroups.com.
To unsubscribe from this group, send email to 
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at 
http://groups.google.com/group/django-users?hl=en.

Managers, Queryset, inheritance and polymorphism

[Amirouche]

Héllo,

I got a problem with manager, some of you may already know it, I try my 
best to like them, if anyone can explain me the purpose of their existence 
I will be so much grateful :)

Like I said, I try my best but:

0) Documentation 
references«default_manager»,
 but I don't find it in the code, is it a documentation 
bug ? 

0bis) What is the purpose of «_default_manager» and «_base_manager» ?

1) What is the purpose of 
«Manager.db»,
 
it's not used in Manager class, so I don't think it's used anywhere else

2) Polymorphism

   - Is there anyone that can debug two level and more of inheritance in 
   
Django-Polymorphic
   - I think this a revision of Django Polymorphic that works with that 
   problem, anyone knows the revision hash ?
   - Do you know any other application that does polymorphism the way I 
   need it (with several level of inheritance) ?
   
If they are answers to question 2, I might no need the answer to the 
following questions, I still would like to know.

I have the following models, manager and querysets 
https://gist.github.com/3826531

According to the code of  Manager in 
manager.py, 
I just need to override «get_query_set», but here is what I get as results, 
the bug is in the second line:

In [14]: PolymorphicQuerySet(Entry)
> Out[14]: [, , , , 
> , , ]
> In [15]: Entry.objects.all()
> Out[15]: []


What am I doing wrong ?

Thanks,


Amirouche

-- 
You received this message because you are subscribed to the Google Groups 
"Django users" group.
To view this discussion on the web visit 
https://groups.google.com/d/msg/django-users/-/G20heNLwu6IJ.
To post to this group, send email to django-users@googlegroups.com.
To unsubscribe from this group, send email to 
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at 
http://groups.google.com/group/django-users?hl=en.