Config::Model::Value - Strongly typed configuration value
version 2.152
use Config::Model;
# 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( steps => 'foo=FOO country=US' );
print $root->report ;
# foo = FOO
# DESCRIPTION: foobar
#
# country = US
# DESCRIPTION: big countries
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 is written in the
target configuration file. ("default" parameter)
- •
- upstream default parameter: specifies a default value that
is used by the application when no information is provided in the
configuration file. This upstream_default value is not written in the
configuration files. Only the "fetch_standard" method returns
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 raises an
exception if the value is not specified (i.e is "undef" or empty
string) 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".
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 known in the
application, but is not written in the configuration file.
- •
- "layered": The value is known by the application
through another mean (e.g. an included configuration file), 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 preset mode
Then there is the value entered by the user. This overrides all kind of
"default" value.
The fetch_standard function returns the "highest" level of default
value, but does not return a custom value, i.e. a value entered by the user.
Value object should not be created directly.
A leaf element must be declared with the following parameters:
- value_type
- Either "boolean", "enum",
"integer", "number", "uniline",
"string", "file", "dir". Mandatory. See
"Value types".
- default
- Specify the default value (optional)
- upstream_default
- Specify a built in default value (optional). I.e a value
known by the application which does not need to be written in the
configuration file.
- write_as
- Array ref. Reserved for boolean value. Specify how to write
a boolean value. Default is "[0,1]" which may not be the most
readable. "write_as" can be specified as
"['false','true']" or "['no','yes']".
- compute
- Computes 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" for
details.
- convert => [uc | lc ]
- When stored, the value is 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 is matched 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 a
default warning message) and instructions to fix the value. A warning is
issued when the value matches the passed regular expression. Valid only
for "string" or "uniline" values. The fix instructions
is evaluated when apply_fixes is called. $_ contains the value to fix. $_
is stored as the new value once the instructions are done. $self contains
the value object. Use with care.
In the example below, any value matching 'foo' is converted in uppercase:
warn_if_match => {
'foo' => {
fix => 'uc;',
msg => 'value $_ contains foo'
},
'BAR' => {
fix =>'lc;',
msg => 'value $_ contains BAR'
}
},
The tests are done in alphabetical order. In the example above,
"BAR" test is done before "foo" test.
$_ is substituted with the bad value when the message is generated.
$std_value is substituted with the standard value (i.e the preset,
computed or default value).
- warn_unless_match
- Hash ref like above. A warning is 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.
- warn_if
- A bit like "warn_if_match". The hash key is not a
regexp but a label to help users. The hash ref contains some Perl code
that is evaluated to perform the test. A warning is issued if the given
code returns true.
$_ contains the value to check. $self contains the
"Config::Model::Value" object (use with care).
The example below warns if value contains a number:
warn_if => {
warn_test => {
code => 'defined $_ && /\d/;',
msg => 'value $_ should not have numbers',
fix => 's/\d//g;'
}
},
Hash key is used in warning message when "msg" is not set:
warn_if => {
'should begin with foo' => {
code => 'defined && /^foo/'
}
}
Any operation or check on file must be done with "file" sub
(otherwise tests will break). This sub returns a Path::Tiny object that
can be used to perform checks. For instance:
warn_if => {
warn_test => {
code => 'not file($_)->exists',
msg => 'file $_ should exist'
}
- warn_unless
- Like "warn_if", but issue a warning when the
given "code" returns false.
The example below warns unless the value points to an existing directory:
warn_unless => {
'missing dir' => {
code => '-d',
fix => "system(mkdir $_);" }
}
- assert
- Like "warn_if". Except that returned value
triggers an error when the given code returns false:
assert => {
test_nb => {
code => 'defined $_ && /\d/;',
msg => 'should not have numbers',
fix => 's/\d//g;'
}
},
hash key can also be used to generate error message when "msg"
parameter is not set.
- grammar
- Setup a Parse::RecDescent grammar to perform validation.
If the grammar does not start with a "check" rule (i.e does not
start with "check: "), the first line of the grammar is modified
to add "check" rule and this rules is set up so the entire value
must match the passed grammar.
I.e. the grammar:
token (oper token)(s?)
oper: 'and' | 'or'
token: 'Apache' | 'CC-BY' | 'Perl'
is changed to
check: token (oper token)(s?) /^\Z/ {$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 $arg[0],
store error message in "${$arg[1]}}" and store warnings in
"${$arg[2]}}".
- replace
- Hash ref. Used for enum to substitute one value with
another. This parameter must be used to enable user to upgrade a
configuration with obsolete values. For instance, if the value
"foo" is obsolete and replaced by "foo_better", you
must declare:
replace => { foo => 'foo_better' }
The hash key can also be a regular expression for wider range replacement.
The regexp must match the whole value:
replace => ( 'foo.*' => 'better_foo' }
In this case, a value is replaced by "better_foo" when the
"/^foo.*$/" regexp matches.
- replace_follow
- Path specifying a hash of value element in the
configuration tree. The hash if used in a way similar to the
"replace" parameter. In this case, the replacement is not coded
in the model but specified by the configuration.
- 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'"}
The key of help is used as a regular expression to find the help text
applicable to a value. These regexp are tried from the longest to the
shortest and are matched from the beginning of the string. The key
""."" or "".*"" are fallback used
last.
For instance:
help => {
'foobar' => 'help for values matching /^foobar/',
'foo' => 'help for values matching /^foo/ but not /^foobar/ (used above)',
'.' => 'help for all other values'
}
This modules can check several value types:
- "boolean"
- Accepts values 1 or 0, "yes" or "no",
"true" or "false", and empty string. 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".
- "file"
- A file name or path. A warning is issued if the file does
not exists (or is a directory)
- "dir"
- A directory name or path. A warning is issued if the
directory does not exists (or is a plain file)
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::Warper for an explanation on warp mechanism).
For instance if you declare 2 "Value" element this way:
$model ->create_config_class (
name => "TV_config_class",
element => [
country => {
type => 'leaf',
value_type => 'enum',
choice => [qw/US Europe Japan/]
} ,
tv_standard => { # this example is getting old...
type => 'leaf',
value_type => 'enum',
choice => [ qw/PAL NTSC SECAM/ ]
warp => {
follow => {
# this points to the warp master
c => '- country'
},
rules => {
'$c eq "US"' => {
default => 'NTSC'
},
'$c eq "France"' => {
default => 'SECAM'
},
'$c eq "Japan"' => {
default => 'NTSC'
},
'$c eq "Europe"' => {
default => 'PAL'
},
}
}
} ,
]
);
Setting "country" element to "US" means that
"tv_standard" has a default value set to "NTSC" by the
warp mechanism.
Likewise, the warp mechanism enables you to dynamically change the possible
values of an enum element:
state => {
type => 'leaf',
value_type => 'enum', # example is admittedly silly
warp => {
follow => {
c => '- country'
},
rules => {
'$c eq "US"' => {
choice => ['Kansas', 'Texas' ]
},
'$c eq "Europe"' => {
choice => ['France', 'Spain' ]
},
'$c eq "Japan"' => {
choice => ['Honshu', 'Hokkaido' ]
}
}
}
}
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 loops are not detected and end up in "deep
recursion subroutine" failures.
- •
- avoid "diamond" shaped warp dependencies: the
results depends on the order of the warp algorithm which can be
unpredictable in this case
- •
- 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 is silently ignored during start up and fails at run
time.
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.
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
Returns the object name.
Returns "leaf".
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).
Query legal values (only for enum types). Return an array (possibly empty).
With a parameter, returns the help string applicable to the passed value or
undef.
Without parameter returns a hash ref that contains all the help strings.
Returns a list of information related to the value, like value type, default
value. This should be used to provide some debug information to the user.
For instance, "$val-"get-info> may return:
[ 'type: string', 'mandatory: yes' ]
Returns the error messages of this object (if any)
Returns warning concerning this value. Returns a list in list context and a
string in scalar context.
Parameters: "( value )"
Check the consistency of the value.
"check_value" also accepts named parameters:
- value
- quiet
- When non null, check does 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.
Returns the number of fixes that can be applied to the current value.
Applies the fixes to suppress the current warnings.
Parameters: "( [ value => foo ] )"
Like "check_value".
Also displays warnings on STDOUT unless "silent" parameter is set to
1. In this case,user is expected to retrieve them with
"warning_msg".
Without "value" argument, this method checks the value currently
stored.
Accept a mode parameter. This function checks if the mode is accepted by
"fetch" method. Returns an error message if not. For instance:
if (my $err = $val->is_bad_mode('foo')) {
croak "my_function: $err";
}
This method is intented as a helper to avoid duplicating the list of accepted
modes for functions that want to wrap fetch methods (like
Config::Model::Dumper or Config::Model::DumpAsData)
Parameters: "( $value )" or "value => ..., check =>
yes|no|skip ), silent => 0|1"
Store value in leaf element. "check" parameter can be used to skip
validation check (default is 'yes'). "silent" can be used to
suppress warnings.
Optional "callback" is now deprecated.
Clear the stored value. Further read returns the default value (or computed or
migrated value).
Parameters: "( $value )"
Called with the same parameters are "store" method.
Load scalar data. Data is forwarded to "store" after checking that the
passed value is not a reference.
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.
Returns the standard value as defined by the configuration model. The standard
value can be either a preset value, a layered value, a computed value, a
default value or a built-in default value.
Return true if the value contains information different from default or upstream
default value.
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. A warning is
issued when a bad value is skipped. Set "check" to
"no" to avoid warnings.
- 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 returns either:
- empty mode parameter (default)
- Value entered by user or default value if the value is
different from upstream_default or layered value. Typically this value is
written in a configuration file.
- backend
- Alias for default mode.
- custom
- The value entered by the user (if different from built in,
preset, computed or default value)
- user
- The value most useful to user: the value that is used by
the application.
- 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)
- layered
- The value found in included files (treated in layered mode:
values specified there are handled as upstream default values). E.g. like
in multistrap config.
- upstream_default
- The upstream_default value. (defined by the configuration
model)
- non_upstream_default
- The custom or preset or computed or default value. Returns
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
- With this mode, "fetch()" behaves like in
"user" mode, but returns "undef" for mandatory values.
Normally, trying to fetch an undefined mandatory value leads to an
exception.
Returns a truncated value when the value is a string or uniline that is too long
to be displayed.
Returns the value entered by the user. Does not use the default or computed
value. Returns undef unless a value was actually stored.
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.
Delete the preset value. (Even out of preset mode). Returns true if other data
are still stored in the value (layered or user data). Returns false otherwise.
Returns the value entered in layered mode. Does not use the default or computed
value. Returns undef unless a value was actually stored in layered mode.
Delete the layered value. (Even out of layered mode). Returns true if other data
are still stored in the value (layered or user data). Returns false otherwise.
Get a value from a directory like path.
Set a value from a directory like path.
bounded_number => {
type => 'leaf',
value_type => 'number',
min => 1,
max => 4,
},
mandatory_string => {
type => 'leaf',
value_type => 'string',
mandatory => 1,
},
mandatory_boolean => {
type => 'leaf',
value_type => 'boolean',
mandatory => 1,
},
Note that the help specification is optional.
enum_with_help => {
type => 'leaf',
value_type => 'enum',
choice => [qw/a b c/],
help => {
a => 'a help'
}
},
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',
},
},
An exception is triggered when the value does not match the "match"
regular expression.
match => {
type => 'leaf',
value_type => 'string',
match => '^foo\d{2}$',
},
match_with_parse_recdescent => {
type => 'leaf',
value_type => 'string',
grammar => q{
token (oper token)(s?)
oper: 'and' | 'or'
token: 'Apache' | 'CC-BY' | 'Perl'
},
},
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'
}
},
},
warn_unless => {
type => 'leaf',
value_type => 'string',
warn_unless_match => {
foo => {
msg => '',
fix => '$_ = "foo".$_;'
}
},
},
always_warn => {
type => 'leaf',
value_type => 'string',
warn => 'Always warn whenever used',
},
See "Examples" in Config::Model::ValueComputer.
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,
},
},
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.
Dominique Dumont, (ddumont at cpan dot org)
Config::Model, Config::Model::Node, Config::Model::AnyId, Config::Model::Warper,
Config::Model::Exception Config::Model::ValueComputer,
Dominique Dumont
This software is Copyright (c) 2005-2022 by Dominique Dumont.
This is free software, licensed under:
The GNU Lesser General Public License, Version 2.1, February 1999