Hi Kate, On 06/18/2015 04:05 AM, Katarzyna Łabędź wrote: > Maybe i didn't understand it correctly. > > I know Django support transactions, but isn't it do it on commit? > I just tried to find the BEGIN statement inside them and i could not > find it - searched through internet and what I found was a bunch of > people asking the same question - where is the begin in the > transactions? So i just figured i ask here. > Why Django don't execute Begin statement ? Isn't it necessary to have a > fully correct transaction?
You are right to be confused, because this is confusing territory. The default behavior of all Python database adapters is "implicit transactions", meaning the underlying database adapter library itself (Python-MySQL, psycopg2, etc) sends a BEGIN automatically as soon as you send your first query. (At least if the library is compliant with PEP 249 [1], the Python database adapter standard, which all adapters used by built-in Django backends are.) Django overrides this and places the underlying connection into autocommit mode (no transactions) by default. But when you request a transaction (by using an 'atomic' block), Django doesn't need to explicitly send BEGIN, it just puts the connection back into the default PEP 249 "implicit transactions" mode, which means the database adapter will send BEGIN automatically as soon as you send a query. So Django never sends a BEGIN itself, just COMMIT or ROLLBACK. In practice, though, you can ignore this implementation detail, and just assume that a BEGIN is sent at the start of any (outer) 'atomic' block (and COMMIT or ROLLBACK) is sent at the end, and you'll be correct. I wrote a blog post [2] which discusses this in more detail. It's about PostgreSQL instead of MySQL, but the part near the beginning about PEP 249 and Django applies equally well to MySQL (I think; I'm not very familiar with transactions on MySQL). Carl [1] https://www.python.org/dev/peps/pep-0249/ [2] http://oddbird.net/2014/06/14/sqlalchemy-postgres-autocommit/ -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To post to this group, send email to django-users@googlegroups.com. Visit this group at http://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/5582E88F.7090709%40oddbird.net. For more options, visit https://groups.google.com/d/optout.
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