How to filter on 2 attributes at once with Django ORM

Question

I have the following models:

class Parent(models.Model):
    item_involved = models.ManyToManyField(Item, through=ItemInvolved)


class ItemInvolved(models.Model):
    parent = models.ForeignKey(Parent, related_name='item_involvement')
    item = models.ForeignKey(Item)
    kind = models.PositiveIntegerField()

I want to retrieve all Parents for which an Item has pk=20 and its ItemInvolved has kind=10.

Edit:

Say I have the following objects:

Parent(pk=1)
Parent(pk=2)
Parent(pk=3)
ItemInvolved(pk=11, parent=1, item=18, kind=10)
ItemInvolved(pk=12, parent=1, item=19, kind=10)
ItemInvolved(pk=13, parent=1, item=20, kind=10)
ItemInvolved(pk=14, parent=2, item=20, kind=10)
ItemInvolved(pk=15, parent=3, item=19, kind=10)
ItemInvolved(pk=16, parent=3, item=20, kind=20)

I need a query that will yield:

[<Parent: 1>, <Parent: 2>]

If any of the below answers helped you, then it's a good practice to accept one! — nik_m, Mar 08 '17 at 12:42

nik_m · Accepted Answer · 2017-03-08T14:06:37.547

1

~~parents = Parent.objects.filter(item=20, item__kind=10)~~

OK. Got it.

parents = Parent.objects.filter(item_involved=20, item_involvement__kind=10)

Further explanation on spanning multi valued relationship.

edited Mar 08 '17 at 14:06

answered Mar 08 '17 at 12:02

nik_m

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This doesn't do what I want. This filters `Parent` by its own `pk`. – Mathieu Marques Mar 08 '17 at 12:12
I mistakenly accepted an edit which changed this. Sorry. Thanks for pointing it out! I just have changed it. – nik_m Mar 08 '17 at 12:14
Added content to clarify what I'm trying to achieve. Also `item__kind` (or rather `item_involved__kind`, I changed the name) shouldn't work. – Mathieu Marques Mar 08 '17 at 13:06
Updated my answer (once again!) – nik_m Mar 08 '17 at 13:33
Can't use `item_involved__kind`. `item_involved` doesn't carry `kind` it's a related field. – Mathieu Marques Mar 08 '17 at 13:38
Its `item_involvement` not `item_involved`! – nik_m Mar 08 '17 at 13:39
https://docs.djangoproject.com/en/dev/topics/db/queries/#spanning-multi-valued-relationships greatly helped me understand why your filter worked. Consider adding it in your answer. :-) – Mathieu Marques Mar 08 '17 at 14:05

score 0 · Answer 2 · answered Mar 08 '17 at 12:11

0

In case you want to log an exception, if the corresponding query is not successful:

try: parent = Parent.objects.get(item=20, item__kind=10) except Exception as e: print "[CRITICAL] <some_view.py> - {}".format(e)

answered Mar 08 '17 at 12:11

Abijith Mg

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How to filter on 2 attributes at once with Django ORM

2 Answers2