Re: group by 3 fields

On Sunday, February 26, 2017 at 12:55:17 PM UTC+1, Daniel Roseman wrote:

You should explain what you want to achieve. Grouping is pointless on its own. In any case, when working with an ORM like Django's it is generally not helpful to think in terms of SQL.

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DR. 

Also forget window functions, triggers, conditionals, pubsub and many other great db features, just because of Django ORM...

Daniel is right - Django ORM will limit your expressions, but not every ORM works that way. SQLAlchemy, in contrast, allows you not only grouping, but also wrap anything into their expression API. 

With Django there is still possibility to do raw queries, nby Model.objects.raw(). I'm doing a complex queries that way, but I'm avoiding spaghetti code by using django-sqltemplate. It allows you to write big SQLs in separate files (also as templates),load using Django templates engine, and finally pass the result directly to Model.objects.raw(), if you want.

You can force grouping, AFAIR. Try to get query object from your queryset, i.e. q=Model.objects.all().query and play with q.group_by or something like that. But this is kind of nasty workaround. I would not recommend doing grouping that way in a project with long-term support.

Generally speaking Django ORM is quite simple, limited and does not work well for more complex projects. I don't want to talk more about this, because my point of view is generally opposite to the "Django Way" (tm). I can just say that I'm using Django ORM as simple mapper for most typical cases, leaving more complex things for better tools.

And, Larry, please never give up and always think about db and data first, then about application layer. Data is most important. It's lifetime is much longer than any app. Continue thinking about grouping, windowing, indexing, fts and so on, and find a way how to handle such things using tools like Django. 

Good luck!

Marcin

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