NAME

JSON::Path::Evaluator - A module that recursively evaluates JSONPath expressions with native support for Javascript-style filters

VERSION

version 1.0.4

SYNOPSIS

use JSON::MaybeXS qw/decode_json/; # Or whatever JSON thing you like. I won't judge.
use JSON::Path::Evaluator qw/evaluate_jsonpath/;

my $obj = decode_json(q(
    { "store": {
        "book": [
          { "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          { "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
          },
          { "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
          },
          { "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
          }
        ],
        "bicycle": {
          "color": "red",
          "price": 19.95
        }
      }
    }
));

my @fiction = evaluate_jsonpath( $obj, q{$..book[?(@.category == "fiction")]});
# @fiction = (
#     {   category => "fiction",
#         author   => "Evelyn Waugh",
#         title    => "Sword of Honour",
#         price    => 12.99
#     },
#     {   category => "fiction",
#         author   => "Herman Melville",
#         title    => "Moby Dick",
#         isbn     => "0-553-21311-3",
#         price    => 8.99
#     },
#     {   category => "fiction",
#         author   => "J. R. R. Tolkien",
#         title    => "The Lord of the Rings",
#         isbn     => "0-395-19395-8",
#         price    => 22.99
#     }
# );

METHODS

new

Constructor for the object-oriented interface to this module. Arguments may be specified in a hash or a hashref.

Args:

root

Required. JSONPath expressions will be evaluated with respect to this. Must be a hashref or an arrayref.

expression

JSONPath expression to evaluate

want_ref

Set this to true if you want a reference to the thing the JSONPath expression matches, rather than the value of said thing. Useful if you want to use this to modify hashrefs / arrayrefs in place.

script_engine

Defaults to "PseudoJS", which is my clever name for a subset of Javascript-like operators for Boolean expressions. See "Filtering with PseudoJS". You may also specify "perl" here, in which case the filter will be treated as Perl code. See "Filtering with Perl".

evaluate_jsonpath

Evaluate a JSONPath expression on the given object. CLASS METHOD.

Args:

$json_object

JSON object for which the expression will be evaluated. If this is a scalar, it will be treated as a JSON string and parsed into the appropriate Perl data structure first.

$expression

JSONPath expression to evaluate on the object.

%args

Misc. arguments to this method. Currently the only supported argument is 'want_ref' - set this to true in order to return a reference to the matched portion of the object, rather than the value of that matched portion.

evaluate

Evaluate a JSONPath expression on the object passed to the constructor. OBJECT METHOD.

Args:

$expression

JSONPath expression to evaluate on the object.

%args

Misc. arguments to this method.

Supported keys:

want_ref

Set this to true in order to return a reference to the matched portion of the object, rather than the value of the matched portion.

want_path

Set this to true in order to return the canonical path(s) to the elements matching the expression.

JSONPath

This code implements the JSONPath specification at JSONPath specification.

JSONPath is a tool, similar to XPath for XML, that allows one to construct queries to pick out parts of a JSON structure.

JSONPath Expressions

From the spec: "JSONPath expressions always refer to a JSON structure in the same way as XPath expression are used in combination with an XML document. Since a JSON structure is usually anonymous and doesn't necessarily have a "root member object" JSONPath assumes the abstract name $ assigned to the outer level object."

Note that in JSONPath square brackets operate on the object or array addressed by the previous path fragment. Indices always start by 0.

Operators

$

the root object/element

@

the current object/element

. or []

child operator

..

recursive descent. JSONPath borrows this syntax from E4X.

*

wildcard. All objects/elements regardless their names.

[]

subscript operator. XPath uses it to iterate over element collections and for predicates. In Javascript and JSON it is the native array operator.

[,]

Union operator in XPath results in a combination of node sets. JSONPath allows alternate names or array indices as a set.

[start:end:step]

array slice operator borrowed from ES4.

?()

applies a filter (script) expression. See Filtering.

()

script expression, using the underlying script engine. Handled the same as "?()".

Filtering

Filters are the most powerful feature of JSONPath. They allow the caller to retrieve data conditionally, similar to Perl's grep operator.

Filters are specified using the '?(' token, terminated by ')'. Anything in between these two tokens is treated as a filter expression. Filter expressions must return a boolean value.

Filtering with PseudoJS

By default, this module uses a limited subset of Javascript expressions to evaluate filters. Using this script engine, specify the filter in the form "<LHS> <operator> <RHS>", or "<LHS>". This latter case will be evaluated as "<LHS> is true".

<LHS> must be a valid JSONPath expression. <RHS> must be a scalar value; comparison of two JSONPath expressions is not supported at this time.

Example:

Using the JSON in SYNOPSIS above and the JSONPath expression $..book[?(@.category == "fiction")], the filter expression @.category == "fiction" will match all values having a value of "fiction" for the key "category".

Regular expressions are supported using the =~ operator, for example: $..book[?(@.category =~ /Fiction/i)]. This is an extension of the Goessner specification introduced by Jayway JsonPath. Other Jayway operators are not currently supported.

Filtering with Perl

When the script engine is set to "perl", filter Using the JSON in SYNOPSIS above and the JSONPath expression $..book[?(@.category == "fiction")],

This is understandably dangerous. Although steps have been taken (Perl expressions are evaluated using Safe and a limited set of permitted opcodes) to reduce the risk, callers should be aware of the risk when using filters.

When filtering in Perl, there are some differences between the JSONPath spec and this implementation.

• JSONPath uses the token '$' to refer to the root node. As this is not valid Perl, this should be replaced with '$root' in a filter expression.

• JSONPath uses the token '@' to refer to the current node. This is also not valid Perl. Use '$_' instead.

AUTHOR

Aurelia Peters <popefelix@gmail.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2022 by Aurelia Peters.

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

cpanm JSON::Path

perl -MCPAN -e shell
install JSON::Path