but is the comment in the code correct ? is "DECLARE CURSOR" required ?
Daniel wrote:
>
> I mentioned this originally, but maybe it wasn't clear. In order to
> have MSSQL perform a select for update the FROM clause must be
> modified. This is comparable to appending FOR UPDATE to the entire
> query in other DBMSs. For example, the following two queries have the
> same effect and show the difference between MySQL and MSSQL
>
> MySQL: SELECT id, name FROM employee WHERE id = 1 FOR UPDATE
> MSSQL: SELECT id, name FROM employee (UPDLOCK) WHERE id=1
>
> In SQLAlchemy 0.5.3, I've noticed that the 'for_update_clause(self,
> select)' function appears to simply append something for the languages
> where it is supported. How/Where would I add the ability in MSSQL to
> modify the FROM clause to have '(UPDLOCK)'?
>
> At the moment the only way I've found to accomplish this is to hand
> write my queries and execute them all directly, as in session.execute
> (query). I'd prefer not to do this since it's functionality that's
> available in MSSQL and appears to have a sensible insertion point in
> SQLAlchemy.
>
> Thanks.
>
> On May 11, 8:40 am, Daniel <daniel.watr...@gmail.com> wrote:
>> Can someone give me an idea about this? Should this be submitted as a
>> bug or feature request?
>>
>> Thanks.
>>
>> On May 7, 3:50 pm, Daniel <daniel.watr...@gmail.com> wrote:
>>
>> > Hello,
>>
>> > I have a transaction that involves a SELECT and subsequent UPDATE. It
>> > is operating against MSSQL. I need to make sure that the row locks so
>> > that other processes may not access it until I have completed my
>> > update, or that they at least fail when trying to UPDATE after the
>> > first transaction commits.
>>
>> > I think that either FOR UPDATE or UPDLOCK would work, but I can't find
>> > a way to make either of them work. In the mmsql.py file I find this
>> > code:
>> > def for_update_clause(self, select):
>> > # "FOR UPDATE" is only allowed on "DECLARE CURSOR" which
>> > SQLAlchemy doesn't use
>> > return ''
>>
>> > This leads me to believe that FOR UPDATE will not work.
>>
>> > I've also tried this
>> > s = select(table.c, table.c.field>0, [text("(UPDLOCK)")])
>> > conn.execute(s)
>>
>> > Rather than producing "SELECT * FROM table (UPDLOCK) where field > 0"
>> > it instead produces "SELECT * FROM table, (UPDLOCK) where field > 0"
>>
>> > That little comman throws the whole thing off. Can anyone suggest a
>> > way for me to accomplish what I'm trying to do in sqlalchemy.
>>
>> > Thanks in advance,
>> > Daniel
> >
>
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