Alias a function parameter in Python / Django model query

Question

I was wondering if it could be possible to query a Django model using aliases of its fields?

for exemple:

class Book(models.Model):
    pub_date = models.DateTimeField(_('Publication Date'),
    ...

class Magazine(models.Model):
    creation_date = models.DateTimeField(_('Publication Date'),
    ...

I can alias the class, which is great:

my_class = Book

then query it as:

my_class.objects.all()

Fine!

I would like to be able to alias the Book.pub_date & Magazine.creation_date as my_pub_date, so I could do:

Book.objects.filter(my_pub_date__gt=some_date) (or my_class.objects.filter(my_pub_date__gt=some_date))

instead of:

Book.objects.filter(pub_date__gt=some_date)

Thanks

It may well be doable, but I think it's probably more trouble than it's worth. How about adding a Book.get_published_after_queryset classmethod? You could do similar methods on Magazine, etc, and then just call my_class.get_pushed_after_queryset(some_date).filter(...). — AdamKG
– AdamKG, Commented Mar 14, 2012 at 12:29

roam · Accepted Answer · 2012-03-14 12:41:34Z

3

Not without a whole lot of effort. And even if it were possible, don't do that if you want to keep your sanity.

In this case I'd use (a) an abstract base class which holds the common information for both models.

class Publication(models.Model):
    pub_date = models.DateField(_('publication date'))
    # other fields

    class Meta:
        abstract = True

class Book(Publication):
    # ...

class Magazine(Publication):
    # ...

Or (b) a single model with a publication_type field, with choices "book" and "magazine".

Or (c) add custom Managers and QuerySets to both models with a method published_after that knows which attribute to use for the filter.

I suggest picking (b) if there's not a lot of difference between books and magazines and (a) if there is.

answered Mar 14, 2012 at 12:41

roam

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1 Comment

ScotchAndSoda Over a year ago

(c) seems to be the best match with my goal. Thanks a lot!

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