NAME

       Config::Model::IdElementReference - Refer to id element(s) and extract keys

VERSION

       version 2.082

SYNOPSIS

        # synopsis shows an example of model of a network to use references

        use Config::Model;

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

        # model of several hosts with several NICs
        $model->create_config_class(
           name      => 'Host',
           'element' => [
               ip_nic => {
                   type       => 'hash',
                   index_type => 'string',
                   cargo      => {
                       type       => 'leaf',
                       value_type => 'uniline',
                   }
               },
           ]
        );

        # model to choose a master host and a master NIC (whatever that may be)
        # among configured hosts. Once these 2 are configured, the model computes
        # the master IP

        $model->create_config_class(
           name => "MyNetwork",

           element => [
               host => {
                   type       => 'hash',
                   index_type => 'string',
                   cargo      => {
                       type              => 'node',
                       config_class_name => 'Host'
                   },
               },

               # master_host is one of the configured hosts
               master_host => {
                   type       => 'leaf',
                   value_type => 'reference', # provided by tConfig::Model::IdElementReference
                   refer_to   => '! host'
               },

               # master_nic is one NIC of the master host
               master_nic => {
                   type              => 'leaf',
                   value_type        => 'reference', # provided by tConfig::Model::IdElementReference
                   computed_refer_to => {            # provided by Config::Model::ValueComputer
                       formula   => '  ! host:$h ip_nic ',
                       variables => { h => '- master_host' }
                   }
               },

               # provided by Config::Model::ValueComputer
               master_ip => {
                   type       => 'leaf',
                   value_type => 'string',
                   compute    => {
                       formula   => '$ip',
                       variables => {
                           h   => '- master_host',
                           nic => '- master_nic',
                           ip  => '! host:$h ip_nic:$nic'
                       }
                   }
               },

           ],
        );

        my $inst = $model->instance(root_class_name => 'MyNetwork' );

        my $root = $inst->config_root ;

        # configure hosts on my network
        my $step = 'host:foo ip_nic:eth0=192.168.0.1 ip_nic:eth1=192.168.1.1 -
                    host:bar ip_nic:eth0=192.168.0.2 ip_nic:eth1=192.168.1.2 -
                    host:baz ip_nic:eth0=192.168.0.3 ip_nic:eth1=192.168.1.3 ';
        $root->load( step => $step );

        print "master host can be one of ",
          join(' ',$root->fetch_element('master_host')->get_choice),"\n" ;
        # prints: master host can be one of bar baz foo

        # choose master host
        $root->load('master_host=bar') ;

        print "master NIC of master host can be one of ",
        join(' ',$root->fetch_element('master_nic')->get_choice),"\n" ;
        # prints: master NIC of master host can be one of eth0 eth1

        # choose master nic
        $root->load('master_nic=eth1') ;

        # check what is the master IP computed by the model
        print "master IP is ",$root->grab_value('master_ip'),"\n";
        # prints master IP is 192.168.1.2

DESCRIPTION

       This class is user by Config::Model::Value to set up an enumerated value where the
       possible choice depends on the key of a Config::Model::HashId or the content of a
       Config::Model::ListId object.

       This class is also used by Config::Model::CheckList to define the checklist items from the
       keys of another hash (or content of a list).

CONSTRUCTOR

       Construction is handled by the calling object (Config::Model::Node).

Config class parameters

       refer_to
           "refer_to" is used to specify a hash element that will be used as a reference.
           "refer_to" points to an array or hash element in the configuration tree using the path
           syntax (See "grab" in Config::Model::Node for details).

       computed_refer_to
           When "computed_refer_to" is used, the path is computed using values from several
           elements in the configuration tree. "computed_refer_to" is a hash with 2 mandatory
           elements: "formula" and "variables".

       The available choice of this (computed or not) reference value is made from the available
       keys of the refered_to hash element or the values of the refered_to array element.

       The example means the the value must correspond to an existing host:

        value_type => 'reference',
        refer_to => '! host'

       This example means the the value must correspond to an existing lan within the host whose
       Id is specified by hostname:

        value_type => 'reference',
        computed_refer_to => { formula => '! host:$a lan',
                               variables => { a => '- hostname' }
                             }

       If you need to combine possibilities from several hash, use the ""+"" token to separate 2
       paths:

        value_type => 'reference',
        computed_refer_to => { formula => '! host:$a lan + ! host:foobar lan',
                               variables => { a => '- hostname' }
                             }

       You can specify "refer_to" or "computed_refer_to" with a "choice" argument so the possible
       enum value will be the combination of the specified choice and the refered_to values.

Methods

   reference_info
       Returns a human readable string with explains how is retrieved the reference. This method
       is mostly used to construct an error messages.

AUTHOR

       Dominique Dumont, (ddumont at cpan dot org)

SEE ALSO

       Config::Model, Config::Model::Value, Config::Model::AnyId, Config::Model::CheckList

AUTHOR

       Dominique Dumont

COPYRIGHT AND LICENSE

       This software is Copyright (c) 2005-2016 by Dominique Dumont.

       This is free software, licensed under:

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