Config::Model::Instance - Instance of configuration tree


version 2.121


 use Config::Model;
 use File::Path ;

 # setup a dummy popcon conf file
 my $wr_dir = '/tmp/etc/';
 my $conf_file = "$wr_dir/popularity-contest.conf" ;

 unless (-d $wr_dir) {
     mkpath($wr_dir, { mode => 0755 }) 
       || die "can't mkpath $wr_dir: $!";
 open(my $conf,"> $conf_file" ) || die "can't open $conf_file: $!";
 $conf->print( qq!MY_HOSTID="aaaaaaaaaaaaaaaaaaaa"\n!,
   qq!USEHTTP="yes" # always http\n!,
 $conf->close ;

 my $model = Config::Model->new;

 # PopCon model is provided. Create a new Config::Model::Instance object
 my $inst = $model->instance (root_class_name   => 'PopCon',
                              root_dir          => '/tmp',
 my $root = $inst -> config_root ;

 print $root->describe;


This module provides an object that holds a configuration tree.


An instance object is created by calling instance method on an existing model. This model can be specified by its application name:

 my $inst = $model->instance (
   # run 'cme list' to get list of applications
   application => 'foo',
   # optional
   instance_name => 'test1'

 my $inst = $model->instance (
   root_class_name => 'SomeRootClass',
   instance_name => 'test1'

The directory (or directories) holding configuration files is specified within the configuration model. For test purpose you can change the "root" directory with root_dir parameter.

Constructor parameters are:


Pseudo root directory where to read and write configuration files (Path::Tiny object or string). Configuration directory specified in model or with config_dir option is appended to this root directory


Path::Tiny object created with root_dir value or with current directory if root_dir is empty.


Directory to read or write configuration file. This parameter must be supplied if not provided by the configuration model. (string)


Specify which backend to use. See "write_back ( ... )" for details


Specify a backend argument that may be retrieved by some backend. Instance is used as a relay and does not use this data.


Specify whether to check value while reading config files. Either:


Check value and throws an error for bad values.


Check value and skip bad value.


Do not check.


When true: write config data back using model order. By default, write items back using the order found in the configuration file. This feature is experimental and not supported by all backends.


Call back this function whenever notify_change is called. Called with arguments: name => <root node element name>, index => <index_value>


Call back this function when show_message is called. By default, messages are displayed on STDOUT.


Returns a list of tree items that currently have an error.


Returns a list of error messages from the tree content.

Note that the root directory specified within the configuration model is overridden by root_dir parameter.

If you need to load configuration data that are not correct, you can use force_load => 1. Then, wrong data are discarded (equivalent to check => 'no' ).


Manage configuration data

modify ( ... )

Calls "load(...)" and then "save".

Takes the same parameter as load plus force_write to force saving configuration file even if no value was modified (default is 0)

load ( ... )

Load configuration tree with configuration data. See "load ( ... )" in Config::Model::Loader for parameters. Returns <$self>.

save ( ... )

Save the content of the configuration tree to configuration files. (alias to write_back)


Returns the root object of the configuration tree.


Scan the tree and apply fixes that are attached to warning specifications. See warn_if_match or warn_unless_match in "" in Config::Model::Value.


Scan the tree and deep check on all elements that support this. Currently only hash or list element have this feature.


Returns 1 (or more) if the instance contains data that needs to be saved. I.e some change were done in the tree that needs to be saved.


In list context, returns a array ref of strings describing the changes. In scalar context, returns a big string. Useful to print.


Print all changes on STDOUT and return the list of changes.


Clear list of changes. Note that changes pending in the configuration tree is not affected. This clears only the list shown to user. Use only for tests.


Returns the number of warning found in the elements of this configuration instance.

update( quiet => (0|1), %args )

Try to run update command on all nodes of the configuration tree. Node without update method are ignored. update prints a message otherwise (unless quiet is true).


Use the steps parameter to retrieve and returns an object from the configuration tree. Forwarded to "grab" in Config::Model::Role::Grab


Use the steps parameter to retrieve and returns the value of a leaf object from the configuration tree. Forwarded to "grab_value" in Config::Model::Role::Grab

searcher ( )

Returns an object dedicated to search an element in the configuration model (respecting privilege level).

This method returns a Config::Model::Searcher object. See Config::Model::Searcher for details on how to handle a search.


This method returns a Config::Model::Iterator object. See Config::Model::Iterator for details.

Arguments are explained in Config::Model::Iterator constructor arguments.


Returns the application name of the instance. (E.g popcon, dpkg ...)

wizard_helper ( ... )

Deprecated. Call "iterator" instead.

Internal methods


Returns the instance name.


Returns which kind of check is performed while reading configuration files. (see check parameter in "CONSTRUCTOR" section)

show_message( string )

Display the message on STDOUT unless a custom function was passed to on_message_cb parameter.


Destroy current configuration tree (with data) and returns a new tree with data (and annotations) loaded from disk.


Returns the model (Config::Model object) of the configuration tree.


Returns the object loading and saving annotations. See Config::Model::Annotation for details.

preset_start ()

All values stored in preset mode are shown to the user as default values. This feature is useful to enter configuration data entered by an automatic process (like hardware scan)

preset_stop ()

Stop preset mode

preset ()

Get preset mode


Clear all preset values stored.

layered_start ()

All values stored in layered mode are shown to the user as default values. This feature is useful to enter configuration data entered by an automatic process (like hardware scan)

layered_stop ()

Stop layered mode

layered ()

Get layered mode


Clear all layered values stored.


Returns 'normal' or 'preset' or 'layered'. Does not take into account initial_load.


Start initial_load mode. This mode tracks the first modifications of the tree done with data read from the configuration file.

Instance is built with initial_load as 1. Read backend clears this value once the first read is done.

Other modifications, when initial_load is zero, are assumed to be user modifications.


Stop initial_load mode. Instance is built with initial_load as 1. Read backend clears this value once the first read is done.


Get initial_load mode

data( kind, [data] )

The data method provide a way to store some arbitrary data in the instance object.

Read and write backend features

Usually, a program based on config model must first create the configuration model, then load all configuration data.

This feature enables you to declare with the model a way to load configuration data (and to write it back). See Config::Model::BackendMgr for details.


Get the preferred backend method for this instance (as passed to the constructor).


Returns a Path::Tiny object for the root directory where configuration data is read from or written to.


Same as root_dir

register_write_back ( node_location )

Register a node path that is called back with write_back method.


Notify that some data has changed in the tree. See "notify_change(...)" in Config::Model::AnyThing for more details.

write_back ( ... )

In summary, save the content of the configuration tree to configuration files.

In more details, write_back trie to run all subroutines registered with register_write_back to write the configuration information. (See Config::Model::BackendMgr for details).

You can specify here another config directory to write configuration data back with config_dir parameter. This overrides the model specifications.

write_back croaks if no write call-back are known.


Dominique Dumont, (ddumont at cpan dot org)


Config::Model, Config::Model::Node, Config::Model::Loader, Config::Model::Searcher, Config::Model::Value,


Dominique Dumont


This software is Copyright (c) 2005-2018 by Dominique Dumont.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999