I need to implement this query using django orm:
update table set field=field+1 where id=id
I don't whant to use this:
o = model.objects.get(id=id)
o.field+=1
o.save()
because it use select and when update, and not thread safe.
How to implement this via orm?
Both the previous answerers have part of the solution: you should use update in conjunction with F():
Model.objects.filter(id=id).update(field=F('field') +1))
Note this does an in-place UPDATE without any need for SELECT at all.
You can use update, details can be found in the documentation
for django v 2.2 (and maybe 3+) SQL statement compilation function could be:
from django.db.models.sql.subqueries import UpdateQuery
def compile_update_query(query_set, update_kwargs):
query = query_set.query.chain(UpdateQuery)
query.add_update_values(update_kwargs)
return str(query)
where query_set is MyShinyModel.objects.filter(id=42) and update_kwargs is a dictionary of model fields to update
If you need to convert the UPDATE ORM query to UPDATE SQL statement without performing it
The update() method is applied instantly and returns the number of rows matched by the query (django 1.8 docs)
def generate_update_sql(queryset, update_kwargs):
""" [checked on django 1.8]
Converts queryset with update_kwargs
like if was: queryset.update(**update_kwargs)
"""
from django.db.models import sql
query = queryset.query.clone(sql.UpdateQuery)
query.add_update_values(update_kwargs)
compiler = query.get_compiler(queryset.db)
sql, params = compiler.as_sql()
return sql % params
Usage
qs = Event.objects.exclude(app='some')
update_kwargs = dict(description='test', action='action')
generate_update_sql(qs, update_kwargs)
Will return
UPDATE `api_event` SET `description` = test, `action` = action WHERE NOT (`api_event`.`app` = some)
