Malcolm Tredinnick wrote:
> On Fri, 2007-05-18 at 23:50 +0200, Olivier Guilyardi wrote:
>>
>> How can I know about the limiting parameters inside a custom manager method?
>>
>> Example:
>>
>> class MyManager(models.Manager):
>> def my_query(self):
>> # How can I find out about offset and length ?
>> cursor.execute("SELECT foo FROM bar LIMIT %d, %d", [offset, length])
>>
>> class MyModel(models.Model)
>> foo = models.CharField(maxlength=200)
>> my_objects = MyManager()
>>
>> # The following should result in offset=0 and length=5 above
>> first_rows = MyModel.my_objects.my_query()[:5]
>>
>> Is this possible?
>
> Not really, no. Python will process the slice arguments ("[:5]") after
> it has called my_query().
Okay, so I suppose a workaround is to pass offset and length as arguments to
my_query()
> The way we work around this in QuerySet is to ensure that every QuerySet
> method (with a few exceptions) returns another QuerySet and we implement
> __getslice__ on the QuerySet class. You would need to emulate that
> behaviour if you really wanted this.
I see. I would need to return an object that implements __getslice__, and
perform my SQL query in this object.
I suppose I may also try to extend the QuerySet class to add my own method. But
this might get rather complex AFAICS in db.models.query.
Thanks for the tips
--
Olivier
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