Set a django object property through a subquery
2
I have an object of type Foo with a ForeignKey to a Bar. Bar has a property called slug.
I can do
myfoo.bar = Bar.objects.get(slug='123')
But this would add an extra query. Is it possible to have Django generate the assignment as a sub-query within the update?
i.e. generate SQL similar to:
UPDATE myfoo SET bar_id = (select id from bar where slug = '123')
django django-orm
edited Nov 14 '18 at 9:28
stellasia
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
add a comment |
2
I have an object of type Foo with a ForeignKey to a Bar. Bar has a property called slug.
I can do
myfoo.bar = Bar.objects.get(slug='123')
But this would add an extra query. Is it possible to have Django generate the assignment as a sub-query within the update?
i.e. generate SQL similar to:
UPDATE myfoo SET bar_id = (select id from bar where slug = '123')
django django-orm
edited Nov 14 '18 at 9:28
stellasia
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
add a comment |
2
2
2
1
I have an object of type Foo with a ForeignKey to a Bar. Bar has a property called slug.
I can do
myfoo.bar = Bar.objects.get(slug='123')
But this would add an extra query. Is it possible to have Django generate the assignment as a sub-query within the update?
i.e. generate SQL similar to:
UPDATE myfoo SET bar_id = (select id from bar where slug = '123')
django django-orm
edited Nov 14 '18 at 9:28
stellasia
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
I have an object of type Foo with a ForeignKey to a Bar. Bar has a property called slug.
I can do
myfoo.bar = Bar.objects.get(slug='123')
But this would add an extra query. Is it possible to have Django generate the assignment as a sub-query within the update?
i.e. generate SQL similar to:
UPDATE myfoo SET bar_id = (select id from bar where slug = '123')
django django-orm
django django-orm
edited Nov 14 '18 at 9:28
stellasia
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
edited Nov 14 '18 at 9:28
stellasia
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
edited Nov 14 '18 at 9:28
stellasia
2,16911126
edited Nov 14 '18 at 9:28
stellasia
2,16911126
edited Nov 14 '18 at 9:28
stellasia
2,16911126
2,16911126
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
asked Nov 14 '18 at 6:27
TordekTordek
7,03122861
7,03122861
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
1
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()
answered Nov 14 '18 at 9:51
mistirumistiru
410112
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to dofoo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can doupdate(a=...,c=[...])it could work.
– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to useupdatewith multiple parameters. Otherwise, you will end up with a lot of queries.
– mistiru
Nov 15 '18 at 8:00
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
1
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()
answered Nov 14 '18 at 9:51
mistirumistiru
410112
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to dofoo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can doupdate(a=...,c=[...])it could work.
– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to useupdatewith multiple parameters. Otherwise, you will end up with a lot of queries.
– mistiru
Nov 15 '18 at 8:00
add a comment |
1
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()
answered Nov 14 '18 at 9:51
mistirumistiru
410112
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to dofoo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can doupdate(a=...,c=[...])it could work.
– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to useupdatewith multiple parameters. Otherwise, you will end up with a lot of queries.
– mistiru
Nov 15 '18 at 8:00
add a comment |
1
1
1
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()
answered Nov 14 '18 at 9:51
mistirumistiru
410112
You can use a Django Subquery expression:
from django.db.models import Subquery
# create the "SELECT id FROM bar WHERE slug = '123' LIMIT 1" subquery
subquery = Bar.objects.filter(slug='123')[:1]
# update only the correct foo object with this subquery
Foo.objects.filter(pk=myfoo.pk).update(bar=Subquery(subquery))
# refresh the variable so that `myfoo.bar` is correct
myfoo.refresh_from_db()
answered Nov 14 '18 at 9:51
mistirumistiru
410112
answered Nov 14 '18 at 9:51
mistirumistiru
410112
answered Nov 14 '18 at 9:51
mistirumistiru
410112
answered Nov 14 '18 at 9:51
mistirumistiru
410112
410112
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to dofoo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can doupdate(a=...,c=[...])it could work.
– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to useupdatewith multiple parameters. Otherwise, you will end up with a lot of queries.
– mistiru
Nov 15 '18 at 8:00
add a comment |
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to dofoo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can doupdate(a=...,c=[...])it could work.
– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to useupdatewith multiple parameters. Otherwise, you will end up with a lot of queries.
– mistiru
Nov 15 '18 at 8:00
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to do
foo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can do update(a=...,c=[...]) it could work.– Tordek
Nov 14 '18 at 22:21
Is it not possible to do it through simple assignment? I.e., I am setting several properties (including a set property) and I'd like to do
foo.a=1; foo.b=2; foo.c=[c,d,e]; foo.bar=Subquery(...). Though if I can do update(a=...,c=[...]) it could work.– Tordek
Nov 14 '18 at 22:21
@Tordek Yes you have to use
update with multiple parameters. Otherwise, you will end up with a lot of queries.– mistiru
Nov 15 '18 at 8:00
@Tordek Yes you have to use
update with multiple parameters. Otherwise, you will end up with a lot of queries.– mistiru
Nov 15 '18 at 8:00
add a comment |
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