json_path 0.3.0-nullsafety

Implementation of JSONPath expressions like "$.store.book[2].price". Can read and set values in parsed JSON objects.

JSONPath for Dart

import 'dart:convert';

import 'package:json_path/json_path.dart';

void main() {
  final json = jsonDecode('''
{
  "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
    }
  }
}  
  ''');

  final prices = JsonPath(r'$..price');

  print('All prices in the store:');

  /// The following code will print:
  ///
  /// $['store']['book'][0]['price']:	8.95
  /// $['store']['book'][1]['price']:	12.99
  /// $['store']['book'][2]['price']:	8.99
  /// $['store']['book'][3]['price']:	22.99
  /// $['store']['bicycle']['price']:	19.95
  prices
      .read(json)
      .map((result) => '${result.path}:\t${result.value}')
      .forEach(print);

  print('\n');

  final bikeColor = JsonPath(r'$.store.bicycle.color');

  print('A copy of the store with repainted bike:');
  print(bikeColor.set(json, 'blue'));

  print('\n');

  print('Note, that the bike in the original store is still red:');
  bikeColor
      .read(json)
      .map((result) => '${result.path}:\t${result.value}')
      .forEach(print);

  print('\n');

  print('It is also possible to modify json in place:');
  final someBooks = JsonPath(r'$.store.book[::2]');
  someBooks.read(json).forEach((match) {
    result.value['title'] = 'Banana';
  });
  print(json);
}

Features and limitations

Generally, this library tries to mimic the reference implementations, except for the filtering. Evaluated expressions are not supported, use named filters instead (see below).

Fields and indices

Both dot-notation ($.store.book[0].title) and bracket-notation ($['store']['book'][2]['title']) are supported.

• The dot-notation only recognizes alphanumeric fields starting with a letter. Use bracket-notation for general cases.
• The bracket-notation supports only single quotes.

Wildcards

Wildcards (*) can be used for objects ($.store.*) and arrays ($.store.book[*]);

Recursion

Use .. to iterate all elements recursively. E.g. $.store..price matches all prices in the store.

Array slice

Use [start:end:step] to filter arrays. Any index can be omitted E.g. $.store.book[3::2] selects all even books starting from the 4th. Negative start and end are also supported.

Unions

Array (book[0,1]) and object (book[author,title,price]) unions are supported. Array unions are always sorted. Object unions support the bracket-notation.

Filtering

Due to the nature of Dart language, filtering expressions like $..book[?(@.price<10)] are NOT supported. Instead, use the callback-kind of filters.

/// Select all elements with price under 20
JsonPath(r'$.store..[?discounted]', filter: {
  'discounted': (e) => e is Map && e['price'] is num && e['price'] < 20
});