cppcms-users

[Cppcms-users] [cppdb] Get the count after select count(*)

[Allan S. <all...@su...>]

Hello,

I want to retrieve the number of row in my table users, so I wrote the 
following

     getUsersCount = sqliteDb.create_prepared_statement(
         "SELECT count(*) as total FROM users "
     );

    int total = getUsersCount.query().get<int>("total");

But I run it, i get the following exception

"2011-07-27 13:20:41 GMT; cppcms, error: Caught exception 
[cppdb::null_value_fetch attempt fetch null column]"

(which is different from the exception i get if i try to get the value 
of a column that does not exists at all)


Am I doing something wrong ?

Regards,

Allan

Re: [Cppcms-users] [cppdb] Get the count after select count(*)

[Artyom B. <art...@ya...>]

> From: Allan SIMON <all...@su...>
> 
> Hello,
> 
> I want to retrieve the number of row in my table users, so I wrote the 
> following
> 
>      getUsersCount = sqliteDb.create_prepared_statement(
>          "SELECT count(*) as total FROM users "
>      );
> 
>     int total = getUsersCount.query().get<int>("total");
> 
> But I run it, i get the following exception
> 
> "2011-07-27 13:20:41 GMT; cppcms, error: Caught exception 
> [cppdb::null_value_fetch attempt fetch null column]"
> 
> (which is different from the exception i get if i try to get the value 
> of a column that does not exists at all)
> 
> 
> Am I doing something wrong ?
> 

Yes.

When you call query() you get a result set that you should 
iterate with next() functions. You looking for row()
that would basically call query() and then call next()

So rewrite it as:

   int total = getUsersCount.row().get<int>("total");

See: http://cppcms.sourceforge.net/sql/cppdb/classcppdb_1_1statement.html#7fd1167898cef7a5592bfd00453ab2f7


By the way:  session::prepare() by default does what create_prepared_statement() does

And the code above can be rewritten nicely as

  sqliteDb <<     
    "SELECT count(*) "
    "FROM users " << cppdb::row 
    >> total;

Artyom