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.\" ========================================================================
.\"
.IX Title "Config::Model::IdElementReference 3pm"
.TH Config::Model::IdElementReference 3pm "2014-09-24" "perl v5.20.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
Config::Model::IdElementReference \- Refer to id element(s) and extract keys
.SH "VERSION"
.IX Header "VERSION"
version 2.061
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& # synopsis shows an example of model of a network to use references
\& 
\& use Config::Model;
\& use Log::Log4perl qw(:easy);
\& Log::Log4perl\->easy_init($WARN);
\&
\& my $model = Config::Model\->new;
\&
\& # model of several hosts with several NICs
\& $model\->create_config_class(
\&    name      => \*(AqHost\*(Aq,
\&    \*(Aqelement\*(Aq => [
\&        ip_nic => {
\&            type       => \*(Aqhash\*(Aq,
\&            index_type => \*(Aqstring\*(Aq,
\&            cargo      => {
\&                type       => \*(Aqleaf\*(Aq,
\&                value_type => \*(Aquniline\*(Aq,
\&            }
\&        },
\&    ]
\& );
\&
\& # 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
\&
\& $model\->create_config_class(
\&    name => "MyNetwork",
\&
\&    element => [
\&        host => {
\&            type       => \*(Aqhash\*(Aq,
\&            index_type => \*(Aqstring\*(Aq,
\&            cargo      => {
\&                type              => \*(Aqnode\*(Aq,
\&                config_class_name => \*(AqHost\*(Aq
\&            },
\&        },
\&
\&        # master_host is one of the configured hosts
\&        master_host => {
\&            type       => \*(Aqleaf\*(Aq,
\&            value_type => \*(Aqreference\*(Aq, # provided by tConfig::Model::IdElementReference
\&            refer_to   => \*(Aq! host\*(Aq
\&        },
\&
\&        # master_nic is one NIC of the master host
\&        master_nic => {
\&            type              => \*(Aqleaf\*(Aq,
\&            value_type        => \*(Aqreference\*(Aq, # provided by tConfig::Model::IdElementReference
\&            computed_refer_to => {            # provided by Config::Model::ValueComputer
\&                formula   => \*(Aq  ! host:$h ip_nic \*(Aq,
\&                variables => { h => \*(Aq\- master_host\*(Aq }
\&            }
\&        },
\&
\&        # provided by Config::Model::ValueComputer
\&        master_ip => {
\&            type       => \*(Aqleaf\*(Aq,
\&            value_type => \*(Aqstring\*(Aq,
\&            compute    => {
\&                formula   => \*(Aq$ip\*(Aq,
\&                variables => {
\&                    h   => \*(Aq\- master_host\*(Aq,
\&                    nic => \*(Aq\- master_nic\*(Aq,
\&                    ip  => \*(Aq! host:$h ip_nic:$nic\*(Aq
\&                }
\&            }
\&        },
\&
\&    ],
\& );
\&
\& my $inst = $model\->instance(root_class_name => \*(AqMyNetwork\*(Aq );
\&
\& my $root = $inst\->config_root ;
\&
\& # configure hosts on my network
\& my $step = \*(Aqhost: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 \*(Aq;
\& $root\->load( step => $step );
\&
\& print "master host can be one of ",
\&   join(\*(Aq \*(Aq,$root\->fetch_element(\*(Aqmaster_host\*(Aq)\->get_choice),"\en" ; 
\& # prints: master host can be one of bar baz foo
\&
\& # choose master host
\& $root\->load(\*(Aqmaster_host=bar\*(Aq) ;
\&
\& print "master NIC of master host can be one of ",
\& join(\*(Aq \*(Aq,$root\->fetch_element(\*(Aqmaster_nic\*(Aq)\->get_choice),"\en" ; 
\& # prints: master NIC of master host can be one of eth0 eth1
\&
\& # choose master nic
\& $root\->load(\*(Aqmaster_nic=eth1\*(Aq) ;
\&
\& # check what is the master IP computed by the model
\& print "master IP is ",$root\->grab_value(\*(Aqmaster_ip\*(Aq),"\en";
\& # prints master IP is 192.168.1.2
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
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).
.SH "CONSTRUCTOR"
.IX Header "CONSTRUCTOR"
Construction is handled by the calling object (Config::Model::Node).
.SH "Config class parameters"
.IX Header "Config class parameters"
.IP "refer_to" 4
.IX Item "refer_to"
\&\f(CW\*(C`refer_to\*(C'\fR is used to specify a hash element that will be used as a
reference. \f(CW\*(C`refer_to\*(C'\fR points to an array or hash element in the
configuration tree using the path syntax (See
\&\*(L"grab\*(R" in Config::Model::Node for details).
.IP "computed_refer_to" 4
.IX Item "computed_refer_to"
When \f(CW\*(C`computed_refer_to\*(C'\fR is used, the path is computed using values
from several elements in the configuration tree. \f(CW\*(C`computed_refer_to\*(C'\fR
is a hash with 2 mandatory elements: \f(CW\*(C`formula\*(C'\fR and \f(CW\*(C`variables\*(C'\fR.
.PP
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.
.PP
The example means the the value must correspond to an existing host:
.PP
.Vb 2
\& value_type => \*(Aqreference\*(Aq,
\& refer_to => \*(Aq! host\*(Aq
.Ve
.PP
This example means the the value must correspond to an existing lan
within the host whose Id is specified by hostname:
.PP
.Vb 4
\& value_type => \*(Aqreference\*(Aq,
\& computed_refer_to => { formula => \*(Aq! host:$a lan\*(Aq, 
\&                        variables => { a => \*(Aq\- hostname\*(Aq }
\&                      }
.Ve
.PP
If you need to combine possibilities from several hash, use the "\f(CW\*(C`+\*(C'\fR"
token to separate 2 paths:
.PP
.Vb 4
\& value_type => \*(Aqreference\*(Aq,
\& computed_refer_to => { formula => \*(Aq! host:$a lan + ! host:foobar lan\*(Aq, 
\&                        variables => { a => \*(Aq\- hostname\*(Aq }
\&                      }
.Ve
.PP
You can specify \f(CW\*(C`refer_to\*(C'\fR or \f(CW\*(C`computed_refer_to\*(C'\fR with a \f(CW\*(C`choice\*(C'\fR
argument so the possible enum value will be the combination of the
specified choice and the refered_to values.
.SH "Methods"
.IX Header "Methods"
.SS "reference_info"
.IX Subsection "reference_info"
Returns a human readable string with explains how is retrieved the
reference. This method is mostly used to construct an error messages.
.SH "AUTHOR"
.IX Header "AUTHOR"
Dominique Dumont, (ddumont at cpan dot org)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Config::Model, Config::Model::Value,
Config::Model::AnyId, Config::Model::CheckList
.SH "AUTHOR"
.IX Header "AUTHOR"
Dominique Dumont
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is Copyright (c) 2014 by Dominique Dumont.
.PP
This is free software, licensed under:
.PP
.Vb 1
\&  The GNU Lesser General Public License, Version 2.1, February 1999
.Ve