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

[Martin B. <mar...@gm...>]

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
>