How to concatenate QuerySets from a list of QuerySet

Question

I come across this syntax on stackoverflow

from itertools import chain 
result_list = list(chain(page_list, article_list, post_list))

I need to concatenate a bunch of QuerySets with something like this:

    prjExpList = list(chain(lvl for lvl in prjlvl))
    prjEnvList = list(chain(env for env in prjEnv))

This gives me an error of

AttributeError: 'QuerySet' object has no attribute '_meta'

My goal is to concatenate a bunch of QuerySets that's stored inside a list prjlvl and prjEnv How do I do that?

Can you give us the full stack trace?

Frank T
– Frank T

2017-07-07 19:27:03 +00:00
Commented Jul 7, 2017 at 19:27 — Frank T
– Frank T, Commented Jul 7, 2017 at 19:27
Try list(chain(prjlvl, prjEnv))

Arpit Solanki
– Arpit Solanki

2017-07-07 19:42:25 +00:00
Commented Jul 7, 2017 at 19:42 — Arpit Solanki
– Arpit Solanki, Commented Jul 7, 2017 at 19:42

Kye · Accepted Answer · 2017-07-08 07:52:06Z

2

Are the QuerySets of the same model? You can just do

combined_queryset = queryset_1 | queryset_2 | queryset_3

To chain them together into one QuerySet. This means you can still do things with the QuerySet in the ORM, which is a big help.

answered Jul 8, 2017 at 7:52

Kye

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Frank T · Accepted Answer · 2017-07-07 19:39:31Z

-1

Try:

prjExpList = list(chain.from_iterable(prjlvl))

Note that itertools.chain() takes a *args list of iterables, and that you can get the same unpacking behavior from the chain.from_iterable() class method.

See: https://docs.python.org/2/library/itertools.html#itertools.chain

edited Jul 7, 2017 at 19:39

answered Jul 7, 2017 at 19:26

Frank T

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3 Comments

Arpit Solanki Over a year ago

This is an overkill . Just using list(queryset) would work fine

Frank T Over a year ago

My understanding is that prjlvl is a list of querysets.

Jasmine Rain Over a year ago

prjlvl is indeed a list of querysets. This solution works!

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