1JSON::Path::Evaluator(3U)ser Contributed Perl DocumentatiJoSnON::Path::Evaluator(3)
2
6 JSON::Path::Evaluator - A module that recursively evaluates JSONPath
7 expressions with native support for Javascript-style filters
8
10 version 0.431
11
13 use JSON::MaybeXS qw/decode_json/; # Or whatever JSON thing you like. I won't judge.
14 use JSON::Path::Evaluator qw/evaluate_jsonpath/;
15 my $obj = decode_json(q(
17 { "store": {
18 "book": [
19 { "category": "reference",
20 "author": "Nigel Rees",
21 "title": "Sayings of the Century",
22 "price": 8.95
23 },
24 { "category": "fiction",
25 "author": "Evelyn Waugh",
26 "title": "Sword of Honour",
27 "price": 12.99
28 },
29 { "category": "fiction",
30 "author": "Herman Melville",
31 "title": "Moby Dick",
32 "isbn": "0-553-21311-3",
33 "price": 8.99
34 },
35 { "category": "fiction",
36 "author": "J. R. R. Tolkien",
37 "title": "The Lord of the Rings",
38 "isbn": "0-395-19395-8",
39 "price": 22.99
40 }
41 ],
42 "bicycle": {
43 "color": "red",
44 "price": 19.95
45 }
46 }
47 }
48 ));
49 my @fiction = evaluate_jsonpath( $obj, q{$..book[?(@.category == "fiction")]});
51 # @fiction = (
52 # { category => "fiction",
53 # author => "Evelyn Waugh",
54 # title => "Sword of Honour",
55 # price => 12.99
56 # },
57 # { category => "fiction",
58 # author => "Herman Melville",
59 # title => "Moby Dick",
60 # isbn => "0-553-21311-3",
61 # price => 8.99
62 # },
63 # { category => "fiction",
64 # author => "J. R. R. Tolkien",
65 # title => "The Lord of the Rings",
66 # isbn => "0-395-19395-8",
67 # price => 22.99
68 # }
69 # );
70
72 new
73 Constructor for the object-oriented interface to this module. Arguments
74 may be specified in a hash or a hashref.
75 Args:
77 root
79 Required. JSONPath expressions will be evaluated with respect to
80 this. Must be a hashref or an arrayref.
81 expression
83 JSONPath expression to evaluate
84 want_ref
86 Set this to true if you want a reference to the thing the JSONPath
87 expression matches, rather than the value of said thing. Useful if
88 you want to use this to modify hashrefs / arrayrefs in place.
89 script_engine
91 Defaults to "PseudoJS", which is my clever name for a subset of
92 Javascript-like operators for Boolean expressions. See "Filtering
93 with PseudoJS". You may also specify "perl" here, in which case the
94 filter will be treated as Perl code. See "Filtering with Perl".
95 evaluate_jsonpath
97 Evaluate a JSONPath expression on the given object. CLASS METHOD.
98 Args:
100 $json_object
102 JSON object for which the expression will be evaluated. If this is
103 a scalar, it will be treated as a JSON string and parsed into the
104 appropriate Perl data structure first.
105 $expression
107 JSONPath expression to evaluate on the object.
108 %args
110 Misc. arguments to this method. Currently the only supported
111 argument is 'want_ref' - set this to true in order to return a
112 reference to the matched portion of the object, rather than the
113 value of that matched portion.
114 evaluate
116 Evaluate a JSONPath expression on the object passed to the constructor.
117 OBJECT METHOD.
118 Args:
120 $expression
122 JSONPath expression to evaluate on the object.
123 %args
125 Misc. arguments to this method.
126 Supported keys:
128 want_ref
130 Set this to true in order to return a reference to the matched
131 portion of the object, rather than the value of the matched
132 portion.
133 want_path
135 Set this to true in order to return the canonical path(s) to
136 the elements matching the expression.
137
139 This code implements the JSONPath specification at JSONPath
140 specification <http://goessner.net/articles/JsonPath/>.
141 JSONPath is a tool, similar to XPath for XML, that allows one to
143 construct queries to pick out parts of a JSON structure.
144 JSONPath Expressions
146 From the spec: "JSONPath expressions always refer to a JSON structure
147 in the same way as XPath expression are used in combination with an XML
148 document. Since a JSON structure is usually anonymous and doesn't
149 necessarily have a "root member object" JSONPath assumes the abstract
150 name $ assigned to the outer level object."
151 Note that in JSONPath square brackets operate on the object or array
153 addressed by the previous path fragment. Indices always start by 0.
154 Operators
156 $ the root object/element
157 @ the current object/element
159 . or []
161 child operator
162 .. recursive descent. JSONPath borrows this syntax from E4X.
164 '*' (literal asterisk)
166 wildcard. All objects/elements regardless their names.
167 [] subscript operator. XPath uses it to iterate over element
169 collections and for predicates. In Javascript and JSON it is the
170 native array operator.
171 [,] Union operator in XPath results in a combination of node sets.
173 JSONPath allows alternate names or array indices as a set.
174 [start:end:step]
176 array slice operator borrowed from ES4.
177 ?() applies a filter (script) expression. See Filtering.
179 () script expression, using the underlying script engine. Handled the
181 same as "?()".
182 Filtering
184 Filters are the most powerful feature of JSONPath. They allow the
185 caller to retrieve data conditionally, similar to Perl's "grep"
186 operator.
187 Filters are specified using the '?(' token, terminated by ')'. Anything
189 in between these two tokens is treated as a filter expression. Filter
190 expressions must return a boolean value.
191 Filtering with PseudoJS
193 By default, this module uses a limited subset of Javascript expressions
195 to evaluate filters. Using this script engine, specify the filter in
196 the form "<LHS> <operator> <RHS>", or "<LHS>". This latter case will be
197 evaluated as "<LHS> is true".
198 <LHS> must be a valid JSONPath expression. <RHS> must be a scalar
200 value; comparison of two JSONPath expressions is not supported at this
201 time.
202 Example:
204 Using the JSON in SYNOPSIS above and the JSONPath expression
206 "$..book[?(@.category == "fiction")]", the filter expression
207 "@.category == "fiction"" will match all values having a value of
208 "fiction" for the key "category".
209 Filtering with Perl
211 When the script engine is set to "perl", filter Using the JSON in
212 SYNOPSIS above and the JSONPath expression "$..book[?(@.category ==
213 "fiction")]",
214 This is understandably dangerous. Although steps have been taken (Perl
216 expressions are evaluated using Safe and a limited set of permitted
217 opcodes) to reduce the risk, callers should be aware of the risk when
218 using filters.
219 When filtering in Perl, there are some differences between the JSONPath
221 spec and this implementation.
222 • JSONPath uses the token '$' to refer to the root node. As this is
224 not valid Perl, this should be
225 replaced with '$root' in a filter expression.
227 • JSONPath uses the token '@' to refer to the current node. This is
229 also not valid Perl. Use '$_'
230 instead.
232
234 Kit Peters <popefelix@gmail.com>
235
237 This software is copyright (c) 2021 by Kit Peters.
238 This is free software; you can redistribute it and/or modify it under
240 the same terms as the Perl 5 programming language system itself.
241perl v5.34.0 2022-01-21 JSON::Path::Evaluator(3)