Re: Circular dependency in forms+views+models

2013-09-02 Thread Marc Tamlyn 
Opened a ticket - https://code.djangoproject.com/ticket/21022


On 2 September 2013 14:37, Russell Keith-Magee wrote:

>
> I agree with Marc -- the fix here is that you should be using a named URL,
> not referencing the view directly. The circular dependency shouldn't exist
> - it should be broken by the dereferencing provided by the URL name. This
> is a feature that was added late in the development of Django (well…
> relatively. Pre 1.0, but after all the core had been laid down), so the
> docs haven't been completely updated to reflect this.
>
> Yours,
> Russ Magee %-)
>
> On Mon, Sep 2, 2013 at 7:53 PM, Marc Tamlyn  wrote:
>
>> I think the main issue here is using the view (name OR instance) as the
>> reference. We really should be pushing naming of urls more in the
>> documentation - they're always mentioned but as a "you might prefer to do
>> this" rather than a "use URL names on every URLpattern and in reverse. You
>> could also use these other methods."
>>
>> The tutorial is now quite good at following these best practices, but the
>> reference docs are not.
>>
>>
>> On 1 September 2013 08:22, Curtis Maloney wrote:
>>
>>> Given both the docs for get_absolute_url and reverse demonstrate using
>>> string references only, I think adding in clarification of why it's
>>> preferred is worthwhile.
>>>
>>> I still find it surprising how often I need to tell people on #django to
>>> not import models just to reference them in relation fields...
>>>
>>> --
>>> Curtis
>>>
>>>
>>>
>>> On 1 September 2013 17:00, Jorge Cardoso Leitao <
>>> jorgecarlei...@gmail.com> wrote:
>>>
 The way I stumbled across this problem was:

 1. views imports models and forms (both are normally needed)

 2. forms imports models (for ModelForm)

 3. models imports views (for get_absolute_url), e.g.:

 *import views*
 *class MyModel(models.Model):*
 * get_absolute_url(reverse(views.myview))*

 which leads to a circular dependency of the form
 views->forms->models->views.

 I searched and there are some questions raised in stackoverflow about
 it, e.g. 
 this
 , 
 this
 .
 This is avoided by removing one of the imports, and in this
 case the candidate is 3., replacing it with a string (e.g.
 'views.myview').

 I propose that we add a note on the documentation of 
 get_absolute_url
 explaining that get_aboslute_url should be coded by returning reverses
 of strings and
 not of functions or classes to avoid circular dependencies.

 There is a ongoing 
 thread
  about
 get_absolute_url and I think these problems are
 somewhat related: this circular dependency is a valid mistake from a
 Django user because models are depending on views, views on forms,
 forms on models.

 Another reason why I think this should be documented is that circular
 dependencies
 are difficult to debug, specially when they occur after modules are
 imported like *import module.*

 This also makes the documentation more consistent: Foreign 
 Key 
 already
 warns about circular dependencies:

 "This sort of reference can be useful when resolving circular import
 dependencies between two applications."

 In summary, I agree that the url's "anti-circular dependency" is
 correctly fixed from the implementation point of view by allowing strings,
 what I'm proposing is just to document why users should use it, i.e.
 what they are useful for, specially in the models' get_absolute_url.

 If no one objects, I can do this.

 Regards,
 Jorge

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Re: Circular dependency in forms+views+models

2013-09-02 Thread Russell Keith-Magee 
I agree with Marc -- the fix here is that you should be using a named URL,
not referencing the view directly. The circular dependency shouldn't exist
- it should be broken by the dereferencing provided by the URL name. This
is a feature that was added late in the development of Django (well…
relatively. Pre 1.0, but after all the core had been laid down), so the
docs haven't been completely updated to reflect this.

Yours,
Russ Magee %-)

On Mon, Sep 2, 2013 at 7:53 PM, Marc Tamlyn  wrote:

> I think the main issue here is using the view (name OR instance) as the
> reference. We really should be pushing naming of urls more in the
> documentation - they're always mentioned but as a "you might prefer to do
> this" rather than a "use URL names on every URLpattern and in reverse. You
> could also use these other methods."
>
> The tutorial is now quite good at following these best practices, but the
> reference docs are not.
>
>
> On 1 September 2013 08:22, Curtis Maloney wrote:
>
>> Given both the docs for get_absolute_url and reverse demonstrate using
>> string references only, I think adding in clarification of why it's
>> preferred is worthwhile.
>>
>> I still find it surprising how often I need to tell people on #django to
>> not import models just to reference them in relation fields...
>>
>> --
>> Curtis
>>
>>
>>
>> On 1 September 2013 17:00, Jorge Cardoso Leitao > > wrote:
>>
>>> The way I stumbled across this problem was:
>>>
>>> 1. views imports models and forms (both are normally needed)
>>>
>>> 2. forms imports models (for ModelForm)
>>>
>>> 3. models imports views (for get_absolute_url), e.g.:
>>>
>>> *import views*
>>> *class MyModel(models.Model):*
>>> * get_absolute_url(reverse(views.myview))*
>>>
>>> which leads to a circular dependency of the form
>>> views->forms->models->views.
>>>
>>> I searched and there are some questions raised in stackoverflow about
>>> it, e.g. 
>>> this
>>> , 
>>> this
>>> .
>>> This is avoided by removing one of the imports, and in this
>>> case the candidate is 3., replacing it with a string (e.g.
>>> 'views.myview').
>>>
>>> I propose that we add a note on the documentation of 
>>> get_absolute_url
>>> explaining that get_aboslute_url should be coded by returning reverses
>>> of strings and
>>> not of functions or classes to avoid circular dependencies.
>>>
>>> There is a ongoing 
>>> thread
>>>  about
>>> get_absolute_url and I think these problems are
>>> somewhat related: this circular dependency is a valid mistake from a
>>> Django user because models are depending on views, views on forms, forms
>>> on models.
>>>
>>> Another reason why I think this should be documented is that circular
>>> dependencies
>>> are difficult to debug, specially when they occur after modules are
>>> imported like *import module.*
>>>
>>> This also makes the documentation more consistent: Foreign 
>>> Key 
>>> already
>>> warns about circular dependencies:
>>>
>>> "This sort of reference can be useful when resolving circular import
>>> dependencies between two applications."
>>>
>>> In summary, I agree that the url's "anti-circular dependency" is
>>> correctly fixed from the implementation point of view by allowing strings,
>>> what I'm proposing is just to document why users should use it, i.e.
>>> what they are useful for, specially in the models' get_absolute_url.
>>>
>>> If no one objects, I can do this.
>>>
>>> Regards,
>>> Jorge
>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "Django developers" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to django-developers+unsubscr...@googlegroups.com.
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>>>
>>
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Re: Circular dependency in forms+views+models

2013-09-02 Thread Marc Tamlyn 
I think the main issue here is using the view (name OR instance) as the
reference. We really should be pushing naming of urls more in the
documentation - they're always mentioned but as a "you might prefer to do
this" rather than a "use URL names on every URLpattern and in reverse. You
could also use these other methods."

The tutorial is now quite good at following these best practices, but the
reference docs are not.


On 1 September 2013 08:22, Curtis Maloney wrote:

> Given both the docs for get_absolute_url and reverse demonstrate using
> string references only, I think adding in clarification of why it's
> preferred is worthwhile.
>
> I still find it surprising how often I need to tell people on #django to
> not import models just to reference them in relation fields...
>
> --
> Curtis
>
>
>
> On 1 September 2013 17:00, Jorge Cardoso Leitao 
> wrote:
>
>> The way I stumbled across this problem was:
>>
>> 1. views imports models and forms (both are normally needed)
>>
>> 2. forms imports models (for ModelForm)
>>
>> 3. models imports views (for get_absolute_url), e.g.:
>>
>> *import views*
>> *class MyModel(models.Model):*
>> * get_absolute_url(reverse(views.myview))*
>>
>> which leads to a circular dependency of the form
>> views->forms->models->views.
>>
>> I searched and there are some questions raised in stackoverflow about it,
>> e.g. 
>> this
>> , 
>> this
>> .
>> This is avoided by removing one of the imports, and in this
>> case the candidate is 3., replacing it with a string (e.g.
>> 'views.myview').
>>
>> I propose that we add a note on the documentation of 
>> get_absolute_url
>> explaining that get_aboslute_url should be coded by returning reverses of
>> strings and
>> not of functions or classes to avoid circular dependencies.
>>
>> There is a ongoing 
>> thread
>>  about
>> get_absolute_url and I think these problems are
>> somewhat related: this circular dependency is a valid mistake from a
>> Django user because models are depending on views, views on forms, forms
>> on models.
>>
>> Another reason why I think this should be documented is that circular
>> dependencies
>> are difficult to debug, specially when they occur after modules are
>> imported like *import module.*
>>
>> This also makes the documentation more consistent: Foreign 
>> Key 
>> already
>> warns about circular dependencies:
>>
>> "This sort of reference can be useful when resolving circular import
>> dependencies between two applications."
>>
>> In summary, I agree that the url's "anti-circular dependency" is
>> correctly fixed from the implementation point of view by allowing strings,
>> what I'm proposing is just to document why users should use it, i.e. what
>> they are useful for, specially in the models' get_absolute_url.
>>
>> If no one objects, I can do this.
>>
>> Regards,
>> Jorge
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "Django developers" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to django-developers+unsubscr...@googlegroups.com.
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>>
>
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Re: Circular dependency in forms+views+models

2013-09-01 Thread Curtis Maloney 
Given both the docs for get_absolute_url and reverse demonstrate using
string references only, I think adding in clarification of why it's
preferred is worthwhile.

I still find it surprising how often I need to tell people on #django to
not import models just to reference them in relation fields...

--
Curtis



On 1 September 2013 17:00, Jorge Cardoso Leitao wrote:

> The way I stumbled across this problem was:
>
> 1. views imports models and forms (both are normally needed)
>
> 2. forms imports models (for ModelForm)
>
> 3. models imports views (for get_absolute_url), e.g.:
>
> *import views*
> *class MyModel(models.Model):*
> * get_absolute_url(reverse(views.myview))*
>
> which leads to a circular dependency of the form
> views->forms->models->views.
>
> I searched and there are some questions raised in stackoverflow about it,
> e.g. 
> this
> , this
> .
> This is avoided by removing one of the imports, and in this
> case the candidate is 3., replacing it with a string (e.g. 'views.myview').
>
> I propose that we add a note on the documentation of 
> get_absolute_url
> explaining that get_aboslute_url should be coded by returning reverses of
> strings and
> not of functions or classes to avoid circular dependencies.
>
> There is a ongoing 
> thread
>  about
> get_absolute_url and I think these problems are
> somewhat related: this circular dependency is a valid mistake from a
> Django user because models are depending on views, views on forms, forms
> on models.
>
> Another reason why I think this should be documented is that circular
> dependencies
> are difficult to debug, specially when they occur after modules are
> imported like *import module.*
>
> This also makes the documentation more consistent: Foreign 
> Key 
> already
> warns about circular dependencies:
>
> "This sort of reference can be useful when resolving circular import
> dependencies between two applications."
>
> In summary, I agree that the url's "anti-circular dependency" is correctly
> fixed from the implementation point of view by allowing strings,
> what I'm proposing is just to document why users should use it, i.e. what
> they are useful for, specially in the models' get_absolute_url.
>
> If no one objects, I can do this.
>
> Regards,
> Jorge
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django developers" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to django-developers+unsubscr...@googlegroups.com.
> To post to this group, send email to django-developers@googlegroups.com.
> Visit this group at http://groups.google.com/group/django-developers.
> For more options, visit https://groups.google.com/groups/opt_out.
>

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