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

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

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

deftest_or_operatorassert_equal[@object['store']['book'][1],@object['store']['book'][3]],JsonPath.new("$..book[?(@['price'] == 13 || @['price'] == 23)]").on(@object)enddeftest_and_operatorassert_equal[],JsonPath.new("$..book[?(@['price'] == 13 && @['price'] == 23)]").on(@object)enddeftest_and_operator_with_more_resultsassert_equal[@object['store']['book'][1]],JsonPath.new("$..book[?(@['price'] < 23 && @['price'] > 9)]").on(@object)end

Selecting Values

It's possible to select results once a query has been defined after the query. For example given this JSON data:

{
"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
}
]
}

... and this query:

"$.store.book[*](category,author)"

... the result can be filtered as such:

[
{
"category":"reference",
"author":"Nigel Rees"
},
{
"category":"fiction",
"author":"Evelyn Waugh"
}
]

Running an individual test

ruby -Ilib:../libtest/test_jsonpath.rb --nametest_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!