On Sep 8, 2011, at 3:32 PM, Vlad K. wrote:
>
> For example the following:
>
> row = session.query(Model).filter_by(pkey=pkey_value).first() or Model()
> row.some_field = 123;
> ...
>
>
> session.query(Model).filter_by(nonprimary_key=some_value).update({...}, false)
> session.merge(row)
> session.flush()
>
> When flush() gets called, the merge() is executed (query sent to DB) before
> the update called above it, in this particular example.
That isn't correct, query.update() emits UPDATE immediately. Do you have a
SQL log illustrating what is being emitted ?
>
>
>
> .oO V Oo.
>
>
> On 09/08/2011 04:37 PM, Michael Bayer wrote:
>> On Sep 8, 2011, at 9:32 AM, Vlad K. wrote:
>>
>>>
>>> As a "by the way" to this question, I've noticed that the order of queries
>>> given before flush() is not preserved for the flush(). Any way to enforce
>>> the order?
>> Trying to parse what this means. Suppose you did a single SELECT, loaded
>> five objects. Then changed them and did a flush. What is the "order of
>> queries" to be preserved?
>>
>> Guessing, perhaps you mean, the order in which a particular object became
>> present in the Session, that's the order in which UPDATE statements should
>> be emitted. UPDATE statements are in fact ordered in terms of the primary
>> key of the row. The reason for this is to minimize the chance of
>> deadlocks. Process A and process B both need to update primary key 1 and
>> 2 in a table. If process A starts with 1 and process B starts with 2, you
>> have a deadlock. So an ordering that is deterministic across
>> transactions, where PK ordering is a pretty good assumption in most cases,
>> is the best behavior here.
>>
>> If you need UPDATE statements in a specific order, you can A. emit flush()
>> specifically against a Session in which you're controlling what's "dirty",
>> B. use query.update(), C. use the Core SQL language instead of the ORM for
>> this particular series of operations (though query.update() likely a happy
>> medium).
>>
>>
>>
>>
>
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