ringemup wrote:
Does that apply to the actual sorting of the data as well? It seems to
me that it's something most efficiently accomplished at the database
level.
If sorting will always be done by field in the model (and not some
complex combination, for example), and SQL orders it how you're
expecting, then I'd say sure, do the sorting with order_by in the model
manager or a custom manager method.
And then... what fields it's sortable on (e.g. you can sort by name,
but not by slug) seems to me to be a property of the model. Not in
terms of which column headers are linked for sorting in the display
(which is very clearly view or template logic), but in terms of what
sorting keywords would be allowed/rejected in the view when processing
the URL -- should the view refer back to the model for that?
Especially since I'm going to require several views for each data type,
and it seems a shame to maintain the sortable-fields list separately
for each one.
On one hand, the fields it's sortable on really is a property of the
view you're looking to write. But it is nice to keep it attached to
the model, much like the admin app views are customizable through your
model. If you try to add, say, a sortable_fields attribute to Meta,
your models won't validate since it checks the Meta class. If I were
doing this, I'd use one of these approaches:
class Payment(models.Model):
...
class Custom:
def sortable_fields = ['amount', 'received_date']
class Payment(models.Model):
...
@classmethod
def get_sortable_fields(cls):
return ['amount', 'received_date']
Now, why not in the manager? Because as far as I can tell, every
method of the default manager performs a query. Sure, you could add
these things there, but it breaks this convention.
So, here's my recommendation:
- Non-saveable fields: Use a custom class attribute or method (these
aren't instance-specific, right?).
- Calculations: Most likely this performs a query. Put it in the
manager.
- Sorting: Take the fields the view wants to sort by and check them
against the sortable fields attribute or method on your model, call
order_by or a custom manager method that does the sorting (since this
will perform a query).
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