NAME

Data::CSel - Select tree node objects using CSS Selector-like syntax

VERSION

This document describes version 0.123 of Data::CSel (from Perl distribution Data-CSel), released on 2020-04-09.

SYNOPSIS

 use Data::CSel qw(csel csel_each);

 my @cells = csel("Table[name=~/data/i] TCell[value != '']:first", $tree);
 for (@cells) { say $_->value }

Using "csel_each":

Using selection object:

 # ditto, but wrap result using a Data::CSel::Selection
 my $res = csel({wrap=>1}, "Table ...", $tree);

 # call method 'foo' of each node object (works even when there are zero nodes
 # in the selection object, or when some nodes do not support the 'foo' method
 $res->foo;

DESCRIPTION

This module lets you use a query language (hereby named CSel) that is similar to CSS Selector to select nodes from a tree of objects.

EXPRESSION SYNTAX

The following is description of the CSel query expression. It is modeled after the CSS Selector syntax with some modification (see "Differences with CSS selector").

An expression is a chain of one or more selectors separated by commas.

A selector is a chain of one or more simple selectors separated by combinators.

A combinator is either: whitespace (descendant combinator), > (child combinator), ~ (general sibling combinator), or + (adjacent sibling combinator). E F, or two elements combined using descendant combinator, means F element descendant of an E element. E > F means F element child of E element. E ~ F means F element preceded by an E element. E + F means F element immediately preceded by an E element.

A simple selector is either a type selector (see "Type selector") or universal selector (see "Universal selector") followed immediately by zero or more attribute selectors (see "Attribute selector" or class selector (see "Class selector"" in ") or ID selector (see "ID selector") or pseudo-classes (see "Pseudo-class"" in "), in any order. Type or universal selector is optional if there is at least one attribute selector or pseudo-class.

Type selector

A type selector is a Perl class/package name.

Example:

 My::Class

will match any My::Class object. Subclasses of My::Class will not be matched, use class selector for that.

Universal selector

A universal selector is * and matches any class/package.

Example:

 *

will match any object.

Attribute selector

An attribute selector filters objects based on the value of their attributes. The syntax is:

 [ATTR]
 [ATTR OP LITERAL]

[ATTR] means to only select objects that have an attribute named ATTR, for example:

 [length]

means to select objects that respond to (can()) length().

Note: to select objects that do not have a specified attribute, you can use the :not pseudo-class (see "Pseudo-class"), for example:

 :not([length])

[ATTR OP LITERAL] means to only select objects that have an attribute named ATTR that has value that matches the expression specified by operator OP and operand LITERAL. For example:

 [length > 12]
 [is_done is true]
 [name =~ /foo/]

Calling methods ATTR can also be replaced by METH() or METH(LITERAL, ...) to allow passing arguments to methods. Note that this specific syntax:

 [METH()]

does not simply mean to select objects that respond to METH, but actually:

 [METH() is true]

For example:

 # select objects that have non-zero length
 [length()]

 # while this means to select objects that have 'length' attribute
 [length]

 # select objects for which the method call returns true
 [has_key('foo')]

Experimental: a chain of attributes is allowed for the attribute, for example:

 [date.month = 12]

will select only objects that has an attribute date, and the value of date is an object that has an attribute month, and the value of month is 12.

Literal

There are several kinds of literals supported.

Numbers. Examples:

 1
 -2.3
 4.5e-6

Boolean:

 true
 false

Null (undef):

 null

String. Either single-quoted (only recognizes the escape sequences \\ and \'):

 'this is a string'
 'this isn\'t hard'

or double-quoted (currently recognizes the escape sequences \\, \", \', \$ [literal $], \t [tab character], \n [newline], \r [linefeed], \f [formfeed], \b [backspace], \a [bell], \e [escape], \0 [null], octal escape e.g. \033, hexadecimal escape e.g. \x1b):

 "This is a string"
 "This isn't hard"
 "Line 1\nLine 2"

For convenience, a word string can be unquoted in expression, e.g.:

 [name = ujang]

is equivalent to:

 [name = 'ujang']

Regex literal. Must be delimited by / ... /, can be followed by zero of more regex modifier characters m, s, i):

 //
 /ab(c|d)/i

Operators

The following are supported operators:

  • eq

    String equality using Perl's eq operator.

    Example:

     Table[title eq "TOC"]

    selects all Table objects that have title() with the value of "TOC".

  • = (or ==)

    Numerical equality using Perl's == operator.

    Example:

     TableCell[length=3]

    selects all TableCell objects that have length() with the value of 3.

    To avoid common trap, will switch to using Perl's eq operator when operand does not look like number, e.g.:

     Table[title = 'foo']

    is the same as:

     Table[title eq 'foo']
  • ne

    String inequality using Perl's ne operator.

    Example:

     Table[title ne "TOC"]

    selects all Table objects that have title() with the value not equal to "TOC".

  • != (or <>)

    Numerical inequality using Perl's != operator.

    Example:

     TableCell[length != 3]
     TableCell[length <> 3]

    selects all TableCell objects that have length() with the value not equal to 3.

    To avoid common trap, will switch to using Perl's ne operator when operand does not look like number, e.g.:

     Table[title != 'foo']

    is the same as:

     Table[title ne 'foo']
  • gt

    String greater-than using Perl's gt operator.

    Example:

     Person[first_name gt "Albert"]

    selects all Person objects that have first_name() with the value asciibetically greater than "Albert".

  • >

    Numerical greater-than using Perl's > operator.

    Example:

     TableCell[length > 3]

    selects all TableCell objects that have length() with the value greater than 3.

    To avoid common trap, will switch to using Perl's gt operator when operand does not look like number, e.g.:

     Person[first_name > 'Albert']

    is the same as:

     Person[first_name gt "Albert"]
  • ge

    String greater-than-or-equal-to using Perl's ge operator.

    Example:

     Person[first_name ge "Albert"]

    selects all Person objects that have first_name() with the value asciibetically greater than or equal to "Albert".

  • >=

    Numerical greater-than-or-equal-to using Perl's >= operator.

    Example:

     TableCell[length >= 3]

    selects all TableCell objects that have length() with the value greater than or equal to 3.

    To avoid common trap, will switch to using Perl's ge operator when operand does not look like number, e.g.:

     Person[first_name >= 'Albert']

    is the same as:

     Person[first_name ge "Albert"]
  • lt

    String less-than using Perl's lt operator.

    Example:

     Person[first_name lt "Albert"]

    selects all Person objects that have first_name() with the value asciibetically less than "Albert".

  • <

    Numerical less-than using Perl's < operator.

    Example:

     TableCell[length < 3]

    selects all TableCell objects that have length() with the value less than 3.

    To avoid common trap, will switch to using Perl's lt operator when operand does not look like number, e.g.:

     Person[first_name < 'Albert']

    is the same as:

     Person[first_name lt "Albert"]
  • le

    String less-than-or-equal-to using Perl's le operator.

    Example:

     Person[first_name le "Albert"]

    selects all Person objects that have first_name() with the value asciibetically less than or equal to "Albert".

  • <=

    Numerical less-than-or-equal-to using Perl's <= operator.

    Example:

     TableCell[length <= 3]

    selects all TableCell objects that have length() with the value less than or equal to 3.

    To avoid common trap, will switch to using Perl's le operator when operand does not look like number, e.g.:

     Person[first_name <= 'Albert']

    is the same as:

     Person[first_name le "Albert"]
  • =~ and !~

    Filter only objects where the attribute named attr has the value matching regular expression value. Operand should be a regex literal. Regex literal must be delimited by //.

    Example:

     Person[first_name =~ /^Al/]

    selects all Person objects that have first_name() with the value matching the regex /^Al/.

     Person[first_name =~ /^al/i]

    Same as previous example except the regex is case-insensitive.

    !~ is the opposite of =~, just like in Perl. It checks whether attr has value that does not match regular expression.

  • is and isnt

    Testing truth value or definedness. Value can be null or boolean literal.

    Example:

     DateTime[is_leap_year is true]

    will select all DateTime objects where its is_leap_year attribute has a true value.

     DateTime[is_leap_year is false]

    will select all DateTime objects where its is_leap_year attribute has a false value.

     Person[age isnt null]

    will select all Person objects where age is defined.

Class selector

A class selector is a . (dot) followed by Perl class/package name.

 .CLASSNAME

It selects all objects that isa() a certain class. The difference with type selector is that inheritance is observed. So:

 .My::Class

will match instances of My::Class as well as subclasses of it.

ID selector

An ID selector is a # (hash) followed by an identifier:

 #ID

It is a special/shortcut form of attribute selector where the attribute is id and the operator is =:

 [id = ID]

The csel() function allows you to configure which attribute to use as the ID attribute, the default is id.

Pseudo-class

A pseudo-class is : (colon) followed by pseudo-class name (a dash-separated word list), and optionally a list of arguments enclosed in parentheses.

 :PSEUDOCLASSNAME
 :PSEUDOCLASSNAME(ARG, ...)

It filters result set based on some criteria. Currently supported pseudo-classes include:

  • :first

    Select only the first object from the result set.

    Example:

     Person[name =~ /^a/i]:first

    selects the first person whose name starts with the letter A.

  • :last

    Select only the last item from the result set.

    Example:

     Person[name =~ /^a/i]:last

    selects the last person whose name starts with the letter A.

  • :first-child

    Select only objects that are the first child of their parent.

  • :last-child

    Select only objects that are the last child of their parent.

  • :only-child

    Select only objects that is the only child of their parent.

  • :nth-child(n)

    Select only objects that are the nth child of their parent.

  • :nth-last-child(n)

    Select only objects that are the nth last child of their parent.

  • :first-of-type

    Select only objects that are the first child of their parent of their type. So if a parent's children is:

     id1(type=T1) id2(T2) id3(T2)

    then both id1 and id2 are first children of their respective types.

  • :last-of-type

    Select only objects that are the last child of their parent of their type.

  • :only-of-type

    Select only objects that are the only child of their parent of their type.

  • :nth-of-type(n)

    Select only objects that are the nth child of their parent of their type.

  • :nth-last-of-type(n)

    Select only objects that are the nth last child of their parent of their type.

  • :root

    Select only root node(s).

  • :empty

    Select only leaf node(s).

  • :not(S)

    Select all objects not matching selector S. S can be a string or an unquoted CSel expression.

    Example:

     :not('.My::Class')
     :not(.My::Class)

    will select all objects that are not of My::Class type.

  • :has(S)

    Select all objects that have a descendant matching selector S. S can be a string or an unquoted CSel expression.

    Example:

     :has('T')
     :not(T)

    will select all objects that have a descendant of type T.

Differences with CSS selector

Type selector can contain double colon (::)

Since Perl package names are separated by ::, CSel allows it in type selector.

Syntax of attribute selector is a bit different

In CSel, the syntax of attribute selector is made simpler and more regular.

There are operators not supported by CSel, but CSel adds more operators from Perl. In particular, the whole substring matching operations like [attr^=val], [attr$=val], [attr*=val], [attr~=val], and [attr|=val] are replaced with the more flexible regex matching instead [attr =~ /re/].

Different pseudo-classes supported

Some CSS pseudo-classes only make sense for a DOM or a visual browser, e.g. :link, :visited, :hover, so they are not supported.

There is no concept of CSS namespaces

CSS namespaces are used when there are foreign elements (e.g. SVG in addition to HTML) and one wants to use the same stylesheet for both. There is no need for something like this CSel, as we deal with only Perl objects.

VARIABLES

@Data::CSel::CLASS_PREFIXES

Array of namespace prefixes to check when matching type in type selector as well as class selector. This is like PATH environment variable in Unix shell. For example, if @CLASS_PREFIXES is ["Foo::Bar", "Baz"], then this expression:

 T

will match class Foo::Bar::T, or Baz::T, or T.

Note that @Data::CSel::CLASS_PREFIXES is consulted after the class_prefixes opton in csel().

FUNCTIONS

csel

Usage:

 $list_or_selection_obj = csel([ \%opts , ] $expr, @tree_nodes)

Select from tree node objects @tree_nodes using CSel expression $expr. Will return a list of mattching node objects (unless when wrap option is true, in which case will return a Data::CSel::Selection object instead). Will die on errors (e.g. syntax error in expression, objects not having the required methods, etc).

A tree node object is any regular Perl object satisfying the following criteria: 1) it supports a parent method which should return a single parent node object, or undef if object is the root node); 2) it supports a children method which should return a list (or an arrayref) of children node objects (where the list/array will be empty for a leaf node). Note: you can use Role::TinyCommons::Tree::Node to enforce this requirement. Note: the parent and children method names can actually be customized, see options.

Known options:

  • class_prefixes => array of str

    Array of namespace prefixes to check when matching type in type selector as well as class selector. This is like PATH environment variable in Unix shell. For example, if class_prefixes is ["Foo::Bar", "Baz"], then this expression:

     T

    will match class Foo::Bar::T, or Baz::T, or T.

    Note that @Data::CSel::CLASS_PREFIXES is also consulted after this class_prefixes option.

  • wrap => bool

    If set to true, instead of returning a list of matching nodes, the function will return a Data::CSel::Selection object instead (which wraps the result, for convenience). See the selection object's documentation for more details.

  • get_parent_method => str

    Example:

     get_parent_method => 'get_parent'

    This option can be used if your node object uses method other than the default parent to get parent node.

  • set_parent_method => str

    Example:

     set_parent_method => 'set_parent'

    This option can be used if your node object uses method other than the default parent to set parent node.

  • get_children_method => str

    Example:

     get_children_method => 'get_children'

    This option can be used if your node object uses method other than the default children to get children nodes.

  • set_children_method => str

    Example:

     set_children_method => 'set_children'

    This option can be used if your node object uses method other than the default children to set children nodes.

csel_each

Usage:

 csel_each { say $_[0]->value } "expr", $tree;
 csel_each { say $_->value    } {csel_opt1=>..., ...}, "expr", $tree1, $tree2;

Execute callback for every node that matches expression. Basically shortcut for:

 my @nodes = csel(...);
 for (@nodes) { $callback->($_) )}

The callback will retrieve the node either in the first element of @_ or in the localized $_ for convenience.

parse_csel

Usage:

 $hash = parse_csel($expr);

Parse an expression. On success, will return a hash containing parsed information. On failure, will return undef.

FAQ

Can I use csel() against a regular data structure (instead of a tree of objects)?

Use Data::CSel::WrapStruct to create a tree of object from the data structure, then perform csel() on the resulting tree.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Data-CSel.

SOURCE

Source repository is at https://github.com/perlancar/perl-Data-CSel.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Data-CSel

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

CSS4 Selectors Specification, https://www.w3.org/TR/selectors4/.

These modules let you use CSS selector syntax (or its subset) to select nodes of an HTML document: Mojo::DOM (or DOM::Tiny), jQuery, pQuery, HTML::Selector::XPath (or via Web::Query). The last two modules can also handle XPath expression.

CLI to select HTML elements using CSS selector syntax: html-css-sel (from App::html::css::sel).

Similar query languages

These modules let you use XPath (or XPath-like) syntax to select nodes of a data structure: Data::DPath. Like CSS selectors, XPath is another query language to select nodes of a document. XPath specification: https://www.w3.org/TR/xpath/.

These modules let you use JSONPath syntax to select nodes of a data structure: JSON::Path. JSONPath is a query language to select nodes of a JSON document (data structure). JSONPath specification: http://goessner.net/articles/JsonPath.

Data::CSel::WrapStruct

CSel::Examples

Modules that use CSel

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2020, 2019, 2016 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.