JsonPath

This is an implementation of http://goessner.net/articles/JsonPath/.

What is JsonPath?

JsonPath is a way of addressing elements within a JSON object. Similar to xpath of yore, JsonPath lets you traverse a json object and manipulate or access it.

Usage

Command-line

There is stand-alone usage through the binary jsonpath

jsonpath [expression] (file|string)

If you omit the second argument, it will read stdin, assuming one valid JSON object
per line. Expression must be a valid jsonpath expression.

Library

To use JsonPath as a library simply include and get goin'!

require 'jsonpath'

json = "{\"store\":\n  {\"bicycle\":\n    {\"price\":19.95, \"color\":\"red\"},\n    \"book\":[\n      {\"price\":8.95, \"category\":\"reference\", \"title\":\"Sayings of the Century\", \"author\":\"Nigel Rees\"},\n      {\"price\":12.99, \"category\":\"fiction\", \"title\":\"Sword of Honour\", \"author\":\"Evelyn Waugh\"},\n      {\"price\":8.99, \"category\":\"fiction\", \"isbn\":\"0-553-21311-3\", \"title\":\"Moby Dick\", \"author\":\"Herman Melville\",\"color\":\"blue\"},\n      {\"price\":22.99, \"category\":\"fiction\", \"isbn\":\"0-395-19395-8\", \"title\":\"The Lord of the Rings\", \"author\":\"Tolkien\"}\n    ]\n  }\n}\n"

Now that we have a JSON object, let's get all the prices present in the object. We create an object for the path in the following way.

path = JsonPath.new('$..price')

Now that we have a path, let's apply it to the object above.

path.on(json)
# => [19.95, 8.95, 12.99, 8.99, 22.99]

Or on some other object ...

path.on('{"books":[{"title":"A Tale of Two Somethings","price":18.88}]}')
# => [18.88]

You can also just combine this into one mega-call with the convenient JsonPath.on method.

JsonPath.on(json, '$..author')
# => ["Nigel Rees", "Evelyn Waugh", "Herman Melville", "Tolkien"]

Of course the full JsonPath syntax is supported, such as array slices

JsonPath.new('$..book[::2]').on(json)
# => [
#      {"price"=>8.95, "category"=>"reference", "author"=>"Nigel Rees", "title"=>"Sayings of the Century"},
#      {"price"=>8.99, "category"=>"fiction", "author"=>"Herman Melville", "title"=>"Moby Dick", "isbn"=>"0-553-21311-3"}
#    ]

...and evals.

JsonPath.new('$..price[?(@ < 10)]').on(json)
# => [8.95, 8.99]

There is a convenience method, #first that gives you the first element for a JSON object and path.

JsonPath.new('$..color').first(object)
# => "red"

As well, we can directly create an Enumerable at any time using #[].

enum = JsonPath.new('$..color')[object]
# => #<JsonPath::Enumerable:...>
enum.first
# => "red"
enum.any?{ |c| c == 'red' }
# => true

You can optionally prevent eval from being called on sub-expressions by passing in :allow_eval => false to the constructor.

More examples

For more usage examples and variations on paths, please visit the tests. There are some more complex ones as well.

Conditional Operators Are Also Supported

  def test_or_operator
    assert_equal [@object['store']['book'][1], @object['store']['book'][3]], JsonPath.new("$..book[?(@['price'] == 13 || @['price'] == 23)]").on(@object)
  end

  def test_and_operator
    assert_equal [], JsonPath.new("$..book[?(@['price'] == 13 && @['price'] == 23)]").on(@object)
  end

  def test_and_operator_with_more_results
    assert_equal [@object['store']['book'][1]], JsonPath.new("$..book[?(@['price'] < 23 && @['price'] > 9)]").on(@object)
  end

Running an individual test

ruby -Ilib:../lib test/test_jsonpath.rb --name test_wildcard_on_intermediary_element_v6

Manipulation

If you'd like to do substitution in a json object, you can use #gsub or #gsub! to modify the object in place.

JsonPath.for('{"candy":"lollipop"}').gsub('$..candy') {|v| "big turks" }.to_hash

The result will be

{'candy' => 'big turks'}

If you'd like to remove all nil keys, you can use #compact and #compact!. To remove all keys under a certain path, use #delete or #delete!. You can even chain these methods together as follows:

json = '{"candy":"lollipop","noncandy":null,"other":"things"}'
o = JsonPath.for(json).
  gsub('$..candy') {|v| "big turks" }.
  compact.
  delete('$..other').
  to_hash
# => {"candy" => "big turks"}

Contributions

Please feel free to submit an Issue or a Pull Request any time you feel like you would like to contribute. Thank you!