On Thu, Jun 17, 2010 at 8:00 PM, Waldemar Kornewald
<wkornew...@gmail.com> wrote:
> Imagine what the code would look like with parameter passing:
>
> class View(object):
> def __call__(self, request, **kwargs):
> qs = self.get_queryset(request, **kwargs)
> .....
>
> def get_queryset(self, request, **kwargs):
> ...
Why would you hardcore the queryset inside the view? Pass the
pre-filtered queryset to the constructor and use get_objects_or_404 to
filter it basing on what is passed to __call__.
Actually as I see it __call__ is not the best idea:
class GenericView(object):
def __init__(self, queryset):
self.qs = queryset
def details(self, request, id):
obj = get_object_or_404(self.qs, id=id)
return direct_to_template(request, 'details.html', {'object': obj})
def list(self, request):
objs = get_objects_or_404(self.qs)
return direct_to_template(request, 'list.html', {'objects': objs})
# ... and so on
> Now someone writes a reusable view for S3 file management which only
> has one parameter (bucket_name) and publishes the code as an
> open-source project:
>
> class S3View(View):
> def get_queryset(request, bucket_name, **kwargs):
> self.get_bucket(bucket_name)
> ...
> ...
Are you sure you need to pass the bucket name each time you _call_ the
view? I'd pass it at construction time instead.
> Then you want to use his code in your project:
>
> class MyS3View(S3View):
> def get_bucket(self, bucket_name):
> # oh no! I need the request and the other configuration
> paramters here! :(
Request sure, but what other configuration parameters? Default
implementation should under no circumstances pass and silently swallow
**kwargs.
> Now you have a problem because the other developer was too lazy to
> pass request and **kwargs to that little "unimportant" get_bucket
> method. This happens in practice and our job is to come up with a
> design that makes this impossible or very unlikely. If the
> one-instance-per-request solution solves this and saves you from
> typing **kwargs all over the place then it absolutely is better, hands
> down.
See above.
--
Patryk Zawadzki
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