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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