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.\" ========================================================================
.\"
.IX Title "Config::Model::BackendMgr 3pm"
.TH Config::Model::BackendMgr 3pm "2023-08-19" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Config::Model::BackendMgr \- Load configuration node on demand
.SH "VERSION"
.IX Header "VERSION"
version 2.153
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 4
\& # Use BackendMgr to write data in Yaml file
\& # This example requires Config::Model::Backend::Yaml which is now
\& # shipped outside of Config::Model. Please get it on CPAN
\& use Config::Model;
\&
\& # define configuration tree object
\& my $model = Config::Model\->new;
\& $model\->create_config_class(
\&    name    => "Foo",
\&    element => [
\&        [qw/foo bar/] => {
\&            type       => \*(Aqleaf\*(Aq,
\&            value_type => \*(Aqstring\*(Aq
\&        },
\&    ]
\& );
\&
\& $model\->create_config_class(
\&    name => "MyClass",
\&
\&    # rw_config spec is used by Config::Model::BackendMgr
\&    rw_config => {
\&        backend     => \*(Aqyaml\*(Aq,
\&        config_dir  => \*(Aq/tmp/\*(Aq,
\&        file        => \*(Aqmy_class.yml\*(Aq,
\&        auto_create => 1,
\&    },
\&
\&    element => [
\&        [qw/foo bar/] => {
\&            type       => \*(Aqleaf\*(Aq,
\&            value_type => \*(Aqstring\*(Aq
\&        },
\&        hash_of_nodes => {
\&            type       => \*(Aqhash\*(Aq,     # hash id
\&            index_type => \*(Aqstring\*(Aq,
\&            cargo      => {
\&                type              => \*(Aqnode\*(Aq,
\&                config_class_name => \*(AqFoo\*(Aq
\&            },
\&        },
\&    ],
\& );
\&
\& my $inst = $model\->instance( root_class_name => \*(AqMyClass\*(Aq );
\&
\& my $root = $inst\->config_root;
\&
\& # put data
\& my $steps = \*(Aqfoo=FOO hash_of_nodes:fr foo=bonjour \-
\&   hash_of_nodes:en foo=hello \*(Aq;
\& $root\->load( steps => $steps );
\&
\& $inst\->write_back;
\&
\& # now look at file /tmp/my_class.yml
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This class provides a way to specify how to load or store
configuration data within the model.
.PP
With these specifications, all configuration information is read
during creation of a node (which triggers the creation of a backend
manager object) and written back when write_back
method is called either on the instance.
.PP
This load/store can be done with different backends:
.IP "\(bu" 4
Any of the \f(CW\*(C`Config::Model::Backend::*\*(C'\fR classes available on your system.
For instance \f(CW\*(C`Config::Model::Backend::Yaml\*(C'\fR.
.IP "\(bu" 4
\&\f(CW\*(C`cds_file\*(C'\fR: Config dump string (cds) in a file. I.e. a string that describes the
content of a configuration tree is loaded from or saved in a text
file. This format is defined by this project. See
\&\*(L"load string syntax\*(R" in Config::Model::Loader.
.IP "\(bu" 4
\&\f(CW\*(C`perl_file\*(C'\fR: Perl data structure (perl) in a file. See Config::Model::DumpAsData
for details on the data structure. Now handled by Config::Model::Backend::PerlFile
.PP
When needed, \f(CW\*(C`write_back\*(C'\fR method can be called on the instance (See
Config::Model::Instance) to store back all configuration information.
.SH "Backend specification"
.IX Header "Backend specification"
The backend specification is provided as an attribute of a
Config::Model::Node specification. These attributes are optional:
A node without \f(CW\*(C`rw_config\*(C'\fR attribute must rely on another node to
read or save its data.
.PP
When needed (usually for the root node), the configuration class is
declared with a \f(CW\*(C`rw_config\*(C'\fR parameter which specifies the read/write
backend configuration.
.SS "Parameters available for all backends"
.IX Subsection "Parameters available for all backends"
The following parameters are accepted by all backends:
.IP "config_dir" 4
.IX Item "config_dir"
Specify configuration directory. This parameter is optional as the
directory can be hardcoded in the backend class. \f(CW\*(C`config_dir\*(C'\fR beginning
with '\f(CW\*(C`~\*(C'\fR' is munged so \f(CW\*(C`~\*(C'\fR is replaced by \f(CW\*(C`File::HomeDir\->my_data\*(C'\fR.
See File::HomeDir for details.
.IP "file" 4
.IX Item "file"
Specify configuration file name (without the path). This parameter is
optional as the file name can be hardcoded in the backend class.
.Sp
The configuration file name can be specified with \f(CW&index\fR keyword
when a backend is associated to a node contained in a hash. For instance,
with \f(CW\*(C`file\*(C'\fR set to \f(CW\*(C`&index.conf\*(C'\fR:
.Sp
.Vb 5
\& service    # hash element
\&   foo      # hash index
\&     nodeA  # values of nodeA are stored in foo.conf
\&   bar      # hash index
\&     nodeB  # values of nodeB are  stored in bar.conf
.Ve
.Sp
Likewise, the keyword \f(CW&element\fR can be used to specify the file
name. For instance, with \f(CW\*(C`file\*(C'\fR set to \f(CW\*(C`&element\-&index.conf\*(C'\fR:
.Sp
.Vb 5
\& service    # hash element
\&   foo      # hash index
\&     nodeA  # values of nodeA are stored in service.foo.conf
\&   bar      # hash index
\&     nodeB  # values of nodeB are  stored in service.bar.conf
.Ve
.IP "file_mode" 4
.IX Item "file_mode"
\&\f(CW\*(C`file_mode\*(C'\fR parameter can be used to set the mode of the written
file(s). \f(CW\*(C`file_mode\*(C'\fR value can be in any form supported by
\&\*(L"chmod\*(R" in Path::Tiny. Example:
.Sp
.Vb 3
\&  file_mode => 0664,
\&  file_mode => \*(Aq0664\*(Aq,
\&  file_mode => \*(Aqg+w\*(Aq
.Ve
.IP "os_config_dir" 4
.IX Item "os_config_dir"
Specify alternate location of a configuration directory depending on the \s-1OS\s0
(as returned by \f(CW$^O\fR, see \*(L"\s-1PLATFORMS\*(R"\s0 in perlport).
For instance:
.Sp
.Vb 2
\& config_dir => \*(Aq/etc/ssh\*(Aq,
\& os_config_dir => { darwin => \*(Aq/etc\*(Aq }
.Ve
.IP "default_layer" 4
.IX Item "default_layer"
Optional. Specifies where to find a global configuration file that
specifies default values. For instance, this is used by OpenSSH to
specify a global configuration file (\f(CW\*(C`/etc/ssh/ssh_config\*(C'\fR) that is
overridden by user's file:
.Sp
.Vb 5
\& default_layer => {
\&    os_config_dir => { \*(Aqdarwin\*(Aq => \*(Aq/etc\*(Aq },
\&    config_dir    => \*(Aq/etc/ssh\*(Aq,
\&    file          => \*(Aqssh_config\*(Aq
\& }
.Ve
.Sp
Only the 3 above parameters can be specified in \f(CW\*(C`default_layer\*(C'\fR.
.IP "auto_create" 4
.IX Item "auto_create"
By default, an exception is thrown if no read was
successful. This behavior can be overridden by specifying
\&\f(CW\*(C`auto_create => 1\*(C'\fR in one of the backend specification. For instance:
.Sp
.Vb 6
\& rw_config  => {
\&     backend => \*(AqIniFile\*(Aq,
\&     config_dir => \*(Aq/tmp\*(Aq,
\&     file  => \*(Aqfoo.conf\*(Aq,
\&     auto_create => 1
\& },
.Ve
.Sp
Setting \f(CW\*(C`auto_create\*(C'\fR to 1 is necessary to create a configuration
from scratch
.IP "auto_delete" 4
.IX Item "auto_delete"
Delete configuration files that contains no data. (default is to leave an empty file)
.SS "Config::Model::Backend::* backends"
.IX Subsection "Config::Model::Backend::* backends"
Specify the backend name and the parameters of the backend defined
in their documentation.
.PP
For instance:
.PP
.Vb 5
\& rw_config => {
\&     backend     => \*(Aqyaml\*(Aq,
\&     config_dir  => \*(Aq/tmp/\*(Aq,
\&     file        => \*(Aqmy_class.yml\*(Aq,
\& },
.Ve
.PP
See Config::Model::Backend::Yaml for more details for this backend.
.SS "Your own backend"
.IX Subsection "Your own backend"
You can also write a dedicated backend. See
How to write your own backend
for details.
.SH "Test setup"
.IX Header "Test setup"
By default, configurations files are read from the directory specified
by \f(CW\*(C`config_dir\*(C'\fR parameter specified in the model. You may override the
\&\f(CW\*(C`root\*(C'\fR directory for test.
.SH "Methods"
.IX Header "Methods"
.SS "support_annotation"
.IX Subsection "support_annotation"
Returns 1 if at least the backend supports read and write annotations
(aka comments) in the configuration file.
.SH "AUTHOR"
.IX Header "AUTHOR"
Dominique Dumont, (ddumont at cpan dot org)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Config::Model, Config::Model::Instance,
Config::Model::Node, Config::Model::Dumper
.SH "AUTHOR"
.IX Header "AUTHOR"
Dominique Dumont
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is Copyright (c) 2005\-2022 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