Django: Extracting a `Q` object from a `QuerySet`

Question

I have a Django QuerySet, and I want to get a Q object out of it. (i.e. that holds the exact same query as that queryset.)

Is that possible? And if so, how?

Freezedrying

Answer 1

No, but you could create the Q object first, and use that; alternatively, create your query as a dict, and pass that to your filter method and the Q object.

Radioman

Answer 2

This is not exactly what you were asking for, but you can extract the sql from a query set by accessing the query member. For example:

x = somequeryset.query

Then you could use that on a new queryset object to reconstruct the original queryset. This may work better in saving stuff like "values" that are defined for a query set. The defined x is easy to store. I've used this in the past to save user constructed queries/searches that then are run daily with the results emailed to the user.

Curhan

Useful information, thanks. Still not as good as Q, because you can't use &, | and ~ on it, but still good to know. – Freezedrying

Answer 3

Relevant also if you wanted the Q object so you you can reconstruct a complex query by ORing another Q object to it, is that, provided two QuerySets are on the same model, you can OR the QuerySets directly for that same effect. It's worth trying that and examining the SQL before and after.

For example:

qs1 = model.objects.filter(...)
print("qs1: {}".format(qs1.query)
qs2 = model.objects.filter(...)
print("qs2: {}".format(qs1.query)
qs = q1 | q2
print("qs: {}".format(qs.query)

I certainly found your question because I wanted the Q object from the query for this very reason, and discovered on the Django Users Group:

https://groups.google.com/d/msg/django-users/2BuFFMDL0VI/dIih2WRKAgAJ

that QuerySets can be combined in much the same way as Q objects can.

That may or may not be helpful to you, depending on the reason you want that Q object of course.

Homology