Django prefetch related and django hvad

Question

I have the following model and I am using django-hvad for the translations

class FooType(TranslatableModel):
    code = models.CharField(max_length=255, unique=True)
    translations = TranslatedFields(name=models.CharField(max_length=255))

    def __unicode__(self):
        return self.lazy_translation_getter('name')

Any time I ask for the list of hotel types;

It makes following query many times

SELECT ••• FROM "foo_footype_translation" WHERE "foo_foo_type_translation"."master_id" = 159 LIMIT 1

I have to apply prefetch_related any time I call for the unicode. Is there a way for that?

Answer 1

EDIT: From looking at the docs, it looks like you should be using TranslationManager

from hvad.manager import TranslationManager

class FooType(TranslatableModel):
    ...

    objects = TranslationManager()

REF: http://django-hvad.readthedocs.org/en/latest/public/queryset.html#translationqueryset

Answer 2

It's been quite some time since that was asked, but as it's not received a definite answer, some things have changed and others have been refined, I figured I'd add one.

The normal way to work with translatable objects in hvad is to request the translation to be fetched as well. You have a couple of examples in the README page and the documentation as well, but it looks like this:

qs = FooType.objects.language("en").all()

The objects loaded in this way will be fully loaded, including their translation in the given language. Objects with no translation in that language are filtered out.

You may omit the language to use current language (most useful when combined with Django's LocaleMiddleware):

qs = FooType.objects.language().all()

You may also use translated fields transparently, for instance this will return all objects with name foobar in current language:

qs = FooType.objects.language().filter(name__iexact='foobar')

You can also search all languages at once using the 'all' special code. The following line will return all objects with name foobar in any language (objects with such name in several language will be returned once for each matching language):

qs = FooType.objects.language('all').filter(name__iexact='foobar')

If you run Django 1.6 or newer, it is also possible to request an object list in a given language, with a priority-based fallback list, this way:

qs = FooType.objects.language("de").fallbacks("ja", "en")

That would fetch all objects, without filtering any. Objects not translated in German would be loaded in Japanese. If they're not available in Japanese, English is tried next, and if it's not available either, an arbitrary language will be picked (internally, this uses a self-join so only one request is made).

In any case, to use translated fields without incurring a performance penalty you must either go through the language() method or make it implicit (for advanced users only).

The reason this behavior is not default is to keep compatibility with existing codebase: as long as language() is not called, hvad does not touch your query.

Hope it helps.