Config::Model::Value(3User Contributed Perl DocumentatiConfig::Model::Value(3)NAMEConfig::Model::Value - Strongly typed configuration value
VERSION
version 1.235
SYNOPSIS
use Config::Model;
use Log::Log4perl qw(:easy);
Log::Log4perl->easy_init($WARN);
# define configuration tree object
my $model = Config::Model->new;
$model ->create_config_class (
name => "MyClass",
element => [
[qw/foo bar/] => {
type => 'leaf',
value_type => 'string',
description => 'foobar',
},
country => {
type => 'leaf',
value_type => 'enum',
choice => [qw/France US/],
description => 'big countries',
},
],
) ;
my $inst = $model->instance(root_class_name => 'MyClass' );
my $root = $inst->config_root ;
# put data
$root->load( step => 'foo=FOO country=US' );
print $root->report ;
# foo = FOO
# DESCRIPTION: foobar
#
# country = US
# DESCRIPTION: big countries
DESCRIPTION
This class provides a way to specify configuration value with the
following properties:
· Strongly typed scalar: the value can either be an enumerated type,
a boolean, a number, an integer or a string
· default parameter: a value can have a default value specified
during the construction. This default value will be written in the
target configuration file. ("default" parameter)
· upstream default parameter: specifies a default value that will be
used by the application when no information is provided in the
configuration file. This upstream_default value will not written in
the configuration files. Only the "fetch_standard" method will
return the builtin value. This parameter was previously referred as
"built_in" value. This may be used for audit purpose.
("upstream_default" parameter)
· mandatory value: reading a mandatory value will raise an exception
if the value is not specified and has no default value.
· dynamic change of property: A slave value can be registered to
another master value so that the properties of the slave value can
change according to the value of the master value. For instance,
paper size value can be 'letter' for country 'US' and 'A4' for
country 'France'.
· A reference to the Id of a hash of list element. In other word, the
value is an enumerated type where the possible values (choice) is
defined by the existing keys of a has element somewhere in the
tree. See "Value Reference".
Default values
There are several kind of default values. They depend on where these
values are defined (or found).
From the lowest default level to the "highest":
· "upstream_default": The value is knows in the application, but is
not written in the configuration file.
· "default": The value is known by the model, but not by the
application. This value must be written in the configuration file.
· "computed": The value is computed from other configuration
elements. This value must be written in the configuration file.
· "preset": The value is not known by the model or by the
application. But it can be found by an automatic program and stored
while the configuration Config::Model::Instance is in
Config::Model::Instance/"preset_start ()"
Then there is the value entered by the user. This will override all
kind of "default" value.
The fetch_standard function will return the "highest" level of default
value, but will not return a custom value, i.e. a value entered by the
user.
Constructor
Value object should not be created directly.
Value model declaration
A leaf element must be declared with the following parameters:
value_type
Either "boolean", "enum", "integer", "number", "uniline", "string".
Mandatory. See "Value types".
default
Specify the default value (optional)
upstream_default
Specify a built in default value (optional)
compute
Will compute a value according to a formula and other values. By
default a computed value cannot be set. See
Config::Model::ValueComputer for computed value declaration.
migrate_from
This is a special parameter to cater for smooth configuration
upgrade. This parameter can be used to copy the value of a
deprecated parameter to its replacement. See "upgrade"" in " for
details.
convert => [uc | lc ]
When stored, the value will be converted to uppercase (uc) or
lowercase (lc).
min Specify the minimum value (optional, only for integer, number)
max Specify the maximum value (optional, only for integer, number)
mandatory
Set to 1 if the configuration value must be set by the
configuration user (default: 0)
choice
Array ref of the possible value of an enum. Example :
choice => [ qw/foo bar/]
match
Perl regular expression. The value will be match with the regex to
assert its validity. Example "match => '^foo'" means that the
parameter value must begin with "foo". Valid only for "string" or
"uniline" values.
warn_if_match
Hash ref. Keys are made of Perl regular expression. The value can
specify a warning message (leave empty or undefined for default
warning message) and instructions to fix the value. A warning will
be issued when the value match the passed regular expression. Valid
only for "string" or "uniline" values. The fix instructions will be
evaluated when apply_fixes is called. $_ will contain the value to
fix. $_ will be stored as the new value once the instructions are
done.
In the example below, any value matching 'foo' will be converted in
uppercase:
warn_if_match => { 'foo' => { fix =>'uc;' }},
warn_unless_match
Hash ref like above. A warning will be issued when the value does
not match the passed regular expression. Valid only for "string" or
"uniline" values.
warn
String. Issue a warning to user with the specified string any time
a value is set or read.
grammar
Setup a Parse::RecDescent grammar to perform validation.
If the grammar does not start with a "check" rule (i.e does not
start with "check: "), the first line of the grammar will be
modified to add "check" rule and set up this rules so the entire
value must match the passed grammar.
I.e. the grammar:
token (oper token)(s?)
oper: 'and' | 'or'
token: 'Apache' | 'CC-BY' | 'Perl'
will be changed to
check: token (oper token)(s?) /^\Z/ {$return = 1;}
oper: 'and' | 'or'
token: 'Apache' | 'CC-BY' | 'Perl'
The rule is called with Value object and a string reference. So, in
the actions you may need to define, you can call the value object
as $arg[0], store error message in "${$arg[1]}}" and store warnings
in "${$arg[2]}}".
replace
Hash ref. Used for enum to substitute one value with another. This
parameter must be used to enable user to upgrade a configuration
with obsolete values. For instance, if the value "foo" is obsolete
and replaced by "foo_better", you will need to declare:
replace => { foo => 'foo_better' }
The hash key can also be a regular expression for wider range
replacement. The regexp must match the whole value:
replace => ( 'foo.*' => 'better_foo' }
In this case, a value will be replaced by "better_foo" if the
"/^foo.*$/" regexp matches.
refer_to
Specify a path to an id element used as a reference. See Value
Reference for details.
computed_refer_to
Specify a path to an id element used as a computed reference. See
"Value Reference" for details.
warp
See section below: "Warp: dynamic value configuration".
help
You may provide detailed description on possible values with a hash
ref. Example:
help => { oui => "French for 'yes'", non => "French for 'no'"}
Value types
This modules can check several value types:
"boolean"
Accepts values 1 or 0, "yes" or "no", "true" or "false". The value
read back is always 1 or 0.
"enum"
Enum choices must be specified by the "choice" parameter.
"integer"
Enable positive or negative integer
"number"
The value can be a decimal number
"uniline"
A one line string. I.e without "\n" in it.
"string"
Actually, no check is performed with this type.
"reference"
Like an "enum" where the possible values (aka choice) is defined by
another location if the configuration tree. See "Value Reference".
Warp: dynamic value configuration
The Warp functionality enable a "Value" object to change its properties
(i.e. default value or its type) dynamically according to the value of
another "Value" object locate elsewhere in the configuration tree. (See
Config::Model::WarpedThing for an explanation on warp mechanism).
For instance if you declare 2 "Value" element this way:
$model ->create_config_class (
name => "TV_config_class",
element => [
country => {
type => 'leaf',
value_type => 'enum',
choice => [qw/US Europe Japan/]
},
tv_standard => {
type => 'leaf',
value_type => 'enum',
choice => [qw/PAL NTSC SECAM/]
warp => {
follow => { c => '- country' }, # this points to the warp master
rules => {
'$c eq "US"' => { default => 'NTSC' },
'$c eq "France"' => { default => 'SECAM' },
'$c eq "Japan"' => { default => 'NTSC' },
'$c eq "Europe"' => { default => 'PAL' },
}
}
},
]
);
Setting "country" element to "US" will mean that "tv_standard" has a
default value set to "NTSC" by the warp mechanism.
Likewise, the warp mechanism enables you to dynamically change the
possible values of an enum element:
state => {
type => 'leaf',
value_type => 'enum', # example is admittedly silly
warp =>{
follow => { c => '- country' },
rules => {
'$c eq "US"' => { choice => ['Kansas', 'Texas' ]},
'$c eq "Europe"' => { choice => ['France', 'Spain' ]},
'$c eq "Japan"' => { choice => ['Honshu', 'Hokkaido' ]}
}
}
}
Cascaded warping
Warping value can be cascaded: "A" can be warped by "B" which can be
warped by "C". But this feature should be avoided since it can lead to
a model very hard to debug. Bear in mind that:
· Warp loop are not detected and will end up in "deep recursion
subroutine" failures.
· If you declare "diamond" shaped warp dependencies, the results will
depend on the order of the warp algorithm and can be unpredictable.
· The keys declared in the warp rules ("US", "Europe" and "Japan" in
the example above) cannot be checked at start time against the warp
master "Value". So a wrong warp rule key will be silently ignored
during start up and will fail at run time.
Value Reference
To set up an enumerated value where the possible choice depends on the
key of a Config::Model::AnyId object, you must:
· Set "value_type" to "reference".
· Specify the "refer_to" or "computed_refer_to" parameter. See
refer_to parameter.
In this case, a "IdElementReference" object is created to handle the
relation between this value object and the referred Id. See
Config::Model::IdElementReference for details.
Introspection methods
The following methods returns the current value of the parameter of the
value object (as declared in the model unless they were warped):
min
max
mandatory
choice
convert
value_type
default
upstream_default
index_value
element_name
name()
Returns the object name.
get_type
Returns "leaf".
can_store()
Returns true if the value object can be assigned to. Return 0 for a
read-only value (i.e. a computed value with no override allowed).
get_choice()
Query legal values (only for enum types). Return an array (possibly
empty).
get_help ( [ on_value ] )
Returns the help strings passed to the constructor.
With "on_value" parameter, returns the help string dedicated to the
passed value or undef.
Without parameter returns a hash ref that contains all the help
strings.
error_msg
Returns the error messages of this object (if any)
warning_msg
Returns warning concerning this value. Returns a list in list context
and a string in scalar context.
check_value ( value )
Check the consistency of the value. Does not check for undefined
mandatory values.
"check_value" also accepts named parameters:
value
quiet
When non null, check will not try to get extra information from the
tree. This is required in some cases to avoid loops in check,
get_info, get_warp_info, re-check ...
In scalar context, return 0 or 1.
In array context, return an empty array when no error was found. In
case of errors, returns an array of error strings that should be shown
to the user.
has_fixes
Returns the number of fixes that can be applied to the current value.
apply_fixes
Applies the fixes to suppress the current warnings.
check( value )
Like "check_value". Also ensure that mandatory value are defined
Will also display warnings on STDOUT unless "silent" parameter is set
to 1. In this case,user is expected to retrieve them with warning_msg.
Information management
store( value )
Can be called as "value => ..., check => yes|no|skip )"
Store value in leaf element. "check" parameter can be used to skip
validation check.
load_data( scalar_value )
Load scalar data. Data is simply forwarded to store.
fetch_custom
Returns the stored value if this value is different from a standard
setting or built in setting. In other words, returns undef if the
stored value is identical to the default value or the computed value or
the built in value.
fetch_standard
Returns the standard value as defined by the configuration model. The
standard value can be either a preset value, a computed value, a
default value or a built-in default value.
fetch( ... )
Check and fetch value from leaf element. The method can have one
parameter (the fetch mode) or several pairs:
mode
Whether to fetch default, custom, etc value. See below for details
check
Whether to check if the value is valid or not before returning it.
Default is 'yes'. Possible value are
yes Perform check and raise an exception for bad values
skip
Perform check and return undef for bad values
no Do not check and return values even if bad
silent
When set to 1, warning are not displayed on STDOUT. User is
expected to read warnings with warning_msg method.
According to the "mode" parameter, this method will return either:
empty mode parameter (default)
Value entered by user or default value if the value is different
from upstream_default
custom
The value entered by the user (if different from built in, preset,
computed or default value)
preset
The value entered in preset mode
standard
The preset or computed or default or built in value.
default
The default value (defined by the configuration model)
upstream_default
The upstream_default value. (defined by the configuration model)
non_upstream_default
The custom or preset or computed or default value. Will return
undef if either of this value is identical to the upstream_default
value. This feature is useful to reduce data to write in
configuration file.
allow_undef
This mode will accept to return undef for mandatory values.
Normally, trying to fetch an undefined mandatory value leads to an
exception.
user_value
Returns the value entered by the user. Does not use the default or
computed value. Returns undef unless a value was actually stored.
fetch_preset
Returns the value entered in preset mode. Does not use the default or
computed value. Returns undef unless a value was actually stored in
preset mode.
get( path => ..., mode => ... , check => ... )
Get a value from a directory like path.
set( path , value )
Set a value from a directory like path.
Examples
Number with min and max values
bounded_number => {
type => 'leaf',
value_type => 'number',
min => 1,
max => 4,
},
Mandatory value
mandatory_string => {
type => 'leaf',
value_type => 'string',
mandatory => 1,
},
mandatory_boolean => {
type => 'leaf',
value_type => 'boolean',
},
Enum with help associated with each value
Note that the help specification is optional.
enum_with_help => {
type => 'leaf',
value_type => 'enum',
choice => [qw/a b c/],
help => { a => 'a help' }
},
Migrate old obsolete enum value
Legacy values "a1", "c1" and "foo/.*" are replaced with "a", "c" and
"foo/".
with_replace => {
type => 'leaf',
value_type => 'enum',
choice => [qw/a b c/],
replace => {
a1 => 'a',
c1 => 'c',
'foo/.*' => 'foo',
},
},
Enforce value to match a regexp
An exception will be triggered if the value does not match the "match"
regular expression.
match => {
type => 'leaf',
value_type => 'string',
match => '^foo\d{2}$',
},
Enforce value to match a Parse::RecDescent grammar
prd_match => {
type => 'leaf',
value_type => 'string',
grammar => q{
token (oper token)(s?)
oper: 'and' | 'or'
token: 'Apache' | 'CC-BY' | 'Perl'
},
},
Issue a warning if a value matches a regexp
Issue a warning if the string contains upper case letters. Propose a
fix that translate all capital letters to lower case.
warn_if_capital => {
type => 'leaf',
value_type => 'string',
warn_if_match => { '/A-Z/' => { fix => '$_ = lc;' } },
},
A specific warning can be specified:
warn_if_capital => {
type => 'leaf',
value_type => 'string',
warn_if_match => {
'/A-Z/' => {
fix => '$_ = lc;' ,
mesg =>'NO UPPER CASE PLEASE'
}
},
},
Issue a warning if a value does NOT match a regexp
warn_unless => {
type => 'leaf',
value_type => 'string',
warn_unless_match => { foo => { msg => '', fix => '$_ = "foo".$_;' } },
},
Always issue a warning
always_warn => {
type => 'leaf',
value_type => 'string',
warn => 'Always warn whenever used',
},
Computed values
See "Examples" in Config::Model::ValueComputer.
Upgrade
Upgrade is a special case when the configuration of an application has
changed. Some parameters can be removed and replaced by another one. To
avoid trouble on the application user side, Config::Model offers a
possibility to handle the migration of configuration data through a
special declaration in the configuration model.
This declaration must:
· Declare the deprecated parameter with a "status" set to
"deprecated"
· Declare the new parameter with the instructions to load the
semantic content from the deprecated parameter. These instructions
are declared in the "migrate_from" parameters (which is similar to
the "compute" parameter)
Here an example where a URL parameter is changed to a set of 2
parameters (host and path):
'old_url' => { type => 'leaf',
value_type => 'uniline',
status => 'deprecated',
},
'host'
=> { type => 'leaf',
value_type => 'uniline',
# the formula must end with '$1' so the result of the capture is used
# as the host value
migrate_from => { formula => '$old =~ m!http://([\w\.]+)!; $1 ;' ,
variables => { old => '- old_url' } ,
use_eval => 1 ,
},
},
'path' => { type => 'leaf',
value_type => 'uniline',
migrate_from => { formula => '$old =~ m!http://[\w\.]+(/.*)!; $1 ;',
variables => { old => '- old_url' } ,
use_eval => 1 ,
},
},
EXCEPTION HANDLING
When an error is encountered, this module may throw the following
exceptions:
Config::Model::Exception::Model
Config::Model::Exception::Formula
Config::Model::Exception::WrongValue
Config::Model::Exception::WarpError
See Config::Model::Exception for more details.
AUTHOR
Dominique Dumont, (ddumont at cpan dot org)
SEE ALSO
Config::Model, Config::Model::Node, Config::Model::AnyId,
Config::Model::WarpedThing, Exception::Class
Config::Model::ValueComputer,
perl v5.14.1 2011-07-22 Config::Model::Value(3)