Also you posted this in https://groups.google.com/forum/#!msg/django-developers/r7JP_YHsIhM/jmof68XFBAAJ . Please don't repost, keep the conversation in one place.
On 3 October 2017 at 17:00, Aymeric Augustin < [email protected]> wrote: > Hello, > > Since I haven't seen positive feedback from a committer, I'm not convinced > there's consensus about this change. > > Also this doesn't look like a particularly easy topic for a beginner. It > raises the following questions: > > - INSERT ON CONFLICT UPDATE would likely be a better option on Postgres ≥ > 9.5, wouldn't it? > - what about other databases with built-in backends? third-party backends? > - is this implementation really appropriate at any isolation level? > - what are the consequences for performance? > > Best regards, > > -- > Aymeric. > > > 2017-10-03 17:23 GMT+02:00 Дилян Палаузов <[email protected]>: > >> Hello Muhereza, >> >> I assume you understand by now Django quite well and are willing to give >> something "in return". >> >> Currently QuerySet.get_or_create() consists of two SQL commands: SELECT + >> optional INSERT. They cause a concurrent problem, if another >> get_or_create() is called between the SQL statements. >> >> With the Postgresql backend it is possible to reduce the queries to a >> single one. >> >> Consider this table: >> >> CREATE TABLE t ( >> id SERIAL PRIMARY KEY, >> name VARCHAR(10) NOT NULL UNIQUE, >> comment VARCHAR(10)); >> >> The following query can do what get_or_create() currently achieves: >> >> WITH >> maybe_found AS (SELECT * FROM t WHERE t.name='nameD'), >> to_be_inserted AS (SELECT 'nameD' as "name", 'comment13' as "comment"), >> just_inserted AS ( >> INSERT INTO t (name, comment) SELECT * FROM to_be_inserted >> WHERE NOT EXISTS(SELECT * FROM maybe_found) >> RETURNING *) >> SELECT *, FALSE as "created" FROM maybe_found UNION ALL >> SELECT *, TRUE AS "created" FROM just_inserted LIMIT 2; >> >> where "to_be_inserted' contains the values for the new object ('default' >> parameter of get_or_create) and 'nameB' in maybe_found is the criterion >> passed to get(). >> >> The challenge is to integrate the WITH ... SELECT query in Django. As >> guidance I can only suggest looking at the existing code. >> >> Regards >> Дилян >> >> >> On 10/03/2017 10:24 AM, Muhereza Herman wrote: >> >>> Hello, anyone reading this please help me out. >>> am a new developer but i would like to contribute to_*django*_. >>> please guide me on how to do that. thank you. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Django developers (Contributions to Django itself)" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected] <mailto: >>> [email protected]>. >>> To post to this group, send email to [email protected] >>> <mailto:[email protected]>. >>> Visit this group at https://groups.google.com/group/django-developers. >>> To view this discussion on the web visit https://groups.google.com/d/ms >>> gid/django-developers/e6d798ac-4ede-45c4-9f20-ca62f0595131%4 >>> 0googlegroups.com <https://groups.google.com/d/m >>> sgid/django-developers/e6d798ac-4ede-45c4-9f20-ca62f0595131% >>> 40googlegroups.com?utm_medium=email&utm_source=footer>. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Django developers (Contributions to Django itself)" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> Visit this group at https://groups.google.com/group/django-developers. >> To view this discussion on the web visit https://groups.google.com/d/ms >> gid/django-developers/062e270c-85f6-23a5-64a3-b225ddcff3ab%40aegee.org. >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- > You received this message because you are subscribed to the Google Groups > "Django developers (Contributions to Django itself)" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/django-developers. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/django-developers/CANE-7mVgudhd0wDAvX9_uLxFUJ89w2Lge6-0rOh_ > U3hPCc4WnA%40mail.gmail.com > <https://groups.google.com/d/msgid/django-developers/CANE-7mVgudhd0wDAvX9_uLxFUJ89w2Lge6-0rOh_U3hPCc4WnA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Adam -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. 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