On Oct 9, 2008, at 8:40 PM, Moshe C. wrote:
>
> Let's say you have two concurrent processes where each might increment
> some integer field in some table row.
> If you query first and the increment in memory and then update, you
> need to query with_lockmode('update') to avoid the case where both
> processes read the same value and the do the same increment.
> A simpler method is to use SQL s.a. set field = field+1.
>
> Q: How do you generate such SQL with SA ?
with expression language:
engine.execute(table.update().values(field = table.c.field + 1))
with ORM:
myobject.field = MyClass.field + 1
session.flush()
> Is there a better method to do it?
the "atomic" increment is probably fine unless you need the value
beforehand, sequences provide a nice way to get an "atomic"
incrementing value, if your DB provides them.
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