Re: [gnome-db] GdaColumn as a GObject

[Vivien Malerba <vmalerba gmail com>]

2005/9/23, Murray Cumming <murrayc murrayc com>:
> On Thu, 2005-09-22 at 21:53 +0200, Vivien Malerba wrote:
> > 2005/9/22, Murray Cumming <murrayc murrayc com>:
> > > In libgda HEAD, GdaColumn was recently changed to be a GObject, instead
> > > of being a copyable boxed type (struct).
> > >
> > > This makes ownership a little less obvious. For instance, may we ever
> > > use the gda_column_set_*() methods on a GdaColumn that we get from
> > > gda_data_model_describe_column() before passing it to
> > > gda_data_model_append_column()? I guess not, because we are using the
> > > same instance.
> > >
> > > I guess we need to always create a new GdaColumn before using the set
> > > methods, but it seems worth asking/clarifying.
> > >
> > > If we could keep the copy function (removed when it was changed to a
> > > GObject), some things would be easier for me.
> >
> > You're right about that problem, I had not seen it!
> >
> > However it seems that method is not implemented by any of the
> > GdaDataModel* objects, so there are two possibilities there:
> > -> change the API to something like
> > GdaColumn *gda_data_model_append_column (GdaDataModel *model); or
> > -> remore that method completely.
>
> append_column() was just an example chosen at random. I'd guess that it
> affects other uses of this object.
>
> But with
> GdaColumn *gda_data_model_append_column (GdaDataModel *model)
> do you mean that we should then use the gda_column_set() after it has been
> appended? Surely we can't do that at any time, because the actual
> database structure is only changed at certain times.
>
> > I'd vote for the second solution because:
> > -> data models are like tables and the number of columns is known when
> > the object is created (like for the GtkListStore and GtkTreeStore
> > models)
> > -> obviously it has not been used much (otherwise people would have
> > noticed that it was not implemented) and it's always better to have
> > simple and concise API.
> >
> > Tell me what you think and I'll do the changes before 2.0.
>
> I'd prefer that
> - the copy() and equals() methods were re-added.
> - Documentation (and use of const) would show whether a copy would be
> taken. For instance,
>
> /** yadda yadda
>  * @column The description of the new column. This column object will be
> copied.
>  */
> void gda_data_model_append_column (GdaDataModel *model, const GdaColumn*
> column)
>
> though that's not completely unambiguous.
>
> But I don't know the reasons for changing it to a GObject in the first
> place. GObjects are usually for things that you _want_ to share via a
> reference.
>

GObject can also have properties, emit signals which can be usefull to
ensure data integrity.

I've just commited new versions of the GdaDataModel, GdaRow and
GdaColumn which make the API simple and easy to understand.

Just a few axamples:
-> if a user wants to modify a value in a data model, all is required
is get a GdaRow pointer with gda_data_model_get_row() and use
gda_row_set_value() to change the value.
-> if a user wants to add a row, just create a new GdaRow object using
gda_row_new(), call gda_data_model_append_row() and then
g_object_unref (row).
-> if a user wants to add a column, call
gda_data_model_append_column() and the set the properties of the
returned GdaColumn.
-> if a user wants to update a complete row, create a new GdaRow
object or copy an existing one, call gda_data_model_update_row() and
then g_object_unref (row)

Cheers,

Vivien