Re: [gnome-db] gda_connection_execute_command() result

["Vivien Malerba" <vmalerba gmail com>]

On 10/21/06, Murray Cumming <murrayc murrayc com> wrote:
> The documentation for gda_connection_execute_command (pasted below) is
> not clear to me, particularly
>
> "The return value is a GList of #GdaDataModel's, and #GdaParameterList".
>
> This seems to mean that the GList* contains some GdaDataModels and some
> GdaParameterLists. If so, what's the sequence or way to identify each
> element? And what would the GdaParameterList items tell me? Where is
> this demonstrated in example code?

You understood correctly. The returned list can hold pointers to
GdaDataModel or GdaParameterList objects, in the same list.
Identifying them is easily done using GObject's introspection features
such as GDA_IS_DATA_MODEL() or GDA_IS_PARAMETER_LIST().

A GdaDataModel is returned in the list whenever the SQL was a SELECT
query (or a query returning a data set), and a GdaParameterList is
returned whenever the query was something else.

What the GdaParameterList contains is a list of named values which are
described in gda_server_provider_execute_command(), the most usefull
one (and only supported at the moment if I remember) being named
"IMPACTED_ROWS" which contains the number of rows impacted by the
query.

Note that if you know that the command contains a SELECT query, then
you'd better use gda_connection_execute_select_command() and if you
know that the command is not as SELECT query, then you should use
gda_connection_execute_non_select_command().
These two functions are wrapper around the first one and make things
easier to use.

> Please note also that, because it's so odd to have 2 types of element in
> a GList, people are likely to interpret this text as just meaning that
> the params parameter is an output parameter. That guess would be
> reinforced by the missing const for that parameter.

I know it can seem a bit strange but is it worth creating overhead
with a structure such as
struct {
     gboolean this_is_a_data_model;
     union {
            GdaDataModel *model;
            GdaParameterList *plist;
     } data;
}
and returning a list of these structures.

Cheers,

Vivien