On Aug 9, 2013, at 10:45 PM, Mark Eastwood <markeastwoo...@gmail.com> wrote:
> It is easier to describe in code than in words.
absolutely, this is much preferred.
> Can anyone please tell me if there is something that I am doing wrong? is
> this a bug with sqlalchemy?
it's kind of a bug, yes, the biggest bug here is that the docs for
query.update() are very underdetailed in this respect, as there is a huge
caveat regarding multi-table mappings here.
your query will work on MySQL, Postgresql, and SQL Server if you do it like
this:
updated = query.filter(Parent.id==Child.id).update({'value': 4})
this because an UPDATE is traditionally against a single table only, however in
SQLA 0.8 the ability to support so-called "multiple table updates" was added, a
feature supported in very different ways by these three backends. So updating
against "Child", which is really a combination of the "parent, child" tables
particularly since your WHERE criteria is against the parent, puts both tables
into the UPDATE statement, but the mechanism currently does not add the
"joining" criteria for the Parent to Child. Such an UPDATE wasn't even
possible prior to 0.8 and also won't work on backends like SQLite or Oracle at
all since they don't support multi-table updates.
These kinds of issues can be diagnosed by setting echo=True on your Engine,
then looking to see what's actually going wrong with the query.
but we need a ticket for this in trac b.c. the docs don't even provide a hint
of this.
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