Aggregation and annotation using a postgres JSONField

[Austin Pua]

I saw this ​StackOverflow post, and I decided to try it out myself. I can confirm that aggregations and annotations do not work with JSONField. Using values() also does not work. I think it has something to do with how the strings/lookups are parsed.

Is this a bug that can/will be fixed before the official 1.9 release, or is this a feature enhancement for future versions? Is it even possible to implement?

[Tim Graham]

Marc, any ideas about this?

[Marc Tamlyn]

This would be about supporting generic __ lookups in more places. It's not a bug, it's a known restriction of the API for values() and annotate(). Now that transforms are expressions, it's possible that something like this should work:

.annotate(Avg(KeyLookup('key_name', 'field_name')))

but I haven't tried it, so syntax might not be quite right there. I believe that annotate works and values does not, but I may be wrong.

In any case, annotation first and then using that annotation later will generally allow more complex queries than you can use directly.

I'm going to close this for now as the expansion of the ORM to cover things like this does not need another ticket. If you can't find a way to make the above work (or similar) let me know.

[Austin Pua]

I was able to whip something up using the Expression API for the lookup, but it fails when I nest it inside an aggregate. It feels a bit hackish and not Django-ish. The docs can use some more examples and more info on the process flow though. Anyway, thanks for pointing me in the right direction! I will try to tinker with it some more.