Based on the UPDATE query section of Model.save()
, this is another means of limiting the fields which are used in an UPDATE statement and bypassing the check for object existence which is made when you use Model.save()
.
Just make whatever changes you want to your model instance and call update
, passing your instance and the names of any fields to be updated.
Usage example:
import datetime
from forum.models import Topic
from forum.utils.models import update
topic = Topic.objects.get(pk=1)
topic.post_count += 1
topic.last_post_at = datetime.datetime.now()
update(topic, 'post_count', 'last_post_at')
(Originally intended as a comment on Snippet 479, but comments aren't working for me)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | from django.db import connection, transaction
def update(model_instance, *args):
"""
Updates only specified fields of the given model instance.
"""
opts = model_instance._meta
fields = [opts.get_field(f) for f in args]
db_values = [f.get_db_prep_save(f.pre_save(model_instance, False)) for f in fields]
if db_values:
connection.cursor().execute("UPDATE %s SET %s WHERE %s=%%s" % \
(connection.ops.quote_name(opts.db_table),
','.join(['%s=%%s' % connection.ops.quote_name(f.column) for f in fields]),
connection.ops.quote_name(opts.pk.column)),
db_values + opts.pk.get_db_prep_lookup('exact', model_instance.pk))
transaction.commit_unless_managed()
|
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