Re: dh_config_model_upgrade: package upgrade with Config::Model

[Dominique Dumont <domi.dumont@free.fr>]

Le dimanche 13 décembre 2009 17:48:13, Stefano Zacchiroli a écrit :
> Can I write my own upgrade script in Perl and have it play with
> the models involved in the upgrade (i.e., the old model and the new
> model) in the same scripts to migrate from one to the other in some
> ad-hoc way?.
> 

Yes. Using Config::Model::Itself and some (untested) code like (please fasten 
your seat belt): 


my $meta_model = Config::Model -> new();

my $old_meta_inst
  = $meta_model->instance (root_class_name => 'Itself::Model' ,
                           instance_name   => 'old model' ,
                          );
my $old_meta_root = $old_meta_inst -> config_root ;

# create object to load model from files
my $old_rw_obj = Config::Model::Itself -> new(model_object => $old_meta_root);

# now load old model from old model files
$old_rw_obj -> read_all( model_dir  => $old_model_dir,
                         root_model => 'SomeModel',
                       ) ;

# serialise old model
my $old_dump = $old_meta_root->dump_tree;

# create new meta instance to hold new model
my $new_meta_inst
  = $meta_model->instance (root_class_name => 'Itself::Model' ,
                           instance_name   => 'new model' ,
                          );
# still empty model
my $new_meta_root = $new_meta_inst -> config_root ;

# copy old model in new instance
$new_meta_root->load($old_dump);

# customize new model
$new_meta_root->load('class:SomeModel element:foobar default="new default");

#create another rw object
my $new_rw_obj = Config::Model::Itself -> new(model_object => $new_meta_root);

# write the modified model somewhere else
$new_rw_obj -> write_all(model_dir => $new_model_dir,
                         root_model => 'SomeModel',
                        ) ;


Depending on what you want to achieve, you may also directly modify the old 
model in the program with:

$old_meta_root->load('class:SomeModel element:foobar default="new default");

and write the customised model files somewhere else as shown above.

HTH 

Dominique
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