Re: [Cppcms-users] C++DB question regarding "IN"

[Jon F. <jon...@jf...>]

Hi Martin!

Thanks for that. I think I like your idea better than mine. I'll have to 
noodle this some. Your assumption is correct. Typical examples would be a 
form that lists a series of DB records of some kind, with check boxes along 
one side. The user checks the boxes and then selects a bulk action (like 
delete, publish, unpublish, ...) and then clicks the "GO" button. Although 
I was asking in general terms since an "IN" operator has other uses.

THX - Jon

Martin Bürgmann wrote:
> Hi Jon,
>
> I don't fully get what you are doing but I'm assuming you want to
> update rows which the user selected previously on the HTML form.
>
> Indeed this does sound like a bit of a pain. And I don't know of any
> cppdb feature that could help here.
>
> I'd suggest using prepared statements like this:
>
> Start with a std::stringstream with your query and one placeholder
>
>      UPDATE my_table SET field_1="my val" WHERE id IN (?
>
> Next, since you know how many rows N the user selected, append N-1
> times another placeholder
>
>      ,?
>
> So you now have your query with N placeholders
>
>      UPDATE my_table SET field_1="my val" WHERE id IN (?,?,?,?
>
> And then finish it with a paren and semicolon and make a prepared
> statement from it
>
>      cppdb::statement stmt = session_handle << strsteam.str();
>
> Now put all the row IDs in
>
>      for (int rid : vector_of_row_ids)
>          stmt << rid;
>
> And finally execute it
>
>      stmt.exec();
>
> Hope I helped at least a little!
>
> Martin
>
> Am Freitag, den 10.07.2020, 09:48 -0700 schrieb Jon Foster:
>> I've skimmed over the C++DB docs a couple of times and I don't see
>> anything
>> about the best way to build queries using the "in" operator. My use
>> case is
>> doing a bulk "UPDATE" command using "in" to target the set of records
>> I
>> want by a list of integer IDs.  Example query:
>>
>>      UPDATE my_table SET field_1="my val" WHERE id IN (1,3,9);
>>
>> Right now I'm scrubbing strings coming back from an HTML form (via
>> C++CMS)
>> and then building them direct into query string. Seems like C++DB
>> probably
>> already has better way. It seems to be well thought out.
>>
>> TIA - Jon
>>
>
>
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"Init Freedom", Yeah!

Jon Foster
JF Possibilities, Inc.
jo...@jf...
541-410-2760
Making computers work for you!


-- 
Sent from my Devuan Linux workstation -- https://devuan.org/
"Init Freedom", Yeah!

Jon Foster
JF Possibilities, Inc.
jo...@jf...