JSONPath support for Ruby.

For more information on JSONPath, see [Stefan Goessner's blog entry] 1, or the [JS and PHP implementations] 2 on Google Code.

gem install bruce-jsonpath --source 'http://gems.github.com'

JSONPath uses [Treetop] 3 for parsing.

As of 2009-07-17, this implementation passes all tests from the [JS and PHP implementations] 2 (after modifying the script expressions for Ruby) -- in addition to its own expanded test suite.

Execute JSONPath queries against a Ruby data structure (as would be parsed from JSON using the json or yajl gems).

Only one method is needed:

JSONPath.lookup(hash_or_array, path)

It supports hash traversal by key:

JSONPath.lookup({"a" => 1}, '$.a')
# => [1]
JSONPath.lookup({"foo" => {"bar baz" => 2}}, "$.foo['bar baz']")
# => [2]

Array traversal by index, including start:stop:step slices:

JSONPath.lookup([1, 2, [3, 4, 5], 6], '$[2][-2:]')
# => [4, 5]

Wildcards:

JSONPath.lookup({"a" => {"b" => 3, "c" => 2}}, "$.a.*")
# => [3, 2]

Descendant traversal (think // in XPath):

JSONPath.lookup({'e' => 1, 'b' => [{'e' => 3}]}, '$..e')
# => [1, 3]

Peek at the tests for more ideas.

It has experimental support for JSONPath's script expressions, including filters. Since JSONPath uses the underlying language in script expressions, that means we have access to Ruby (supporting arbitrarily complex traversal). As in other JSONPath implementations, @ is replaced by the current node.

lists = [
  [1, 2, 3, 4],
  [5, 6],
  [7, 8, 9, 10]
]
JSONPath.lookup(lists, "$.*[(@.length - 1)]")
=> [4, 6, 10]

And filters:

books = [
  {"name" => 'Bruce', "age" => 29},
  {"name" => "Braedyn", "age" => 3},
  {"name" => "Jamis", "age" => 2},
]
JSONPath.lookup(people, "$[?(@['age'] % 2 == 0)].name")
# => ['Jamis']

For more information, see the the [JSONPath introductory article] 1.

The [project] 4 is hosted on [GitHub] 5, where I gladly accept pull requests.

If you run into any problems, please either (in order of preference) post something on the [issue tracker] 6, send me a message on GitHub, or email me.

Copyright (c) 2009 Bruce Williams, based on work by Stefan Goessner. See LICENSE.