jq.cr

thin JSON::Any wrapper to emulate jq for Crystal.

see Wiki for examples

breaking changes

• v0.5.0 : (breaking-change) mapping: parse Time without formats.

crystal versions

• v0.5.1 : 0.24 or lower
• v0.6.0 : 0.25 .. 0.27
• v0.8.0 : 0.27 .. 0.35
• v0.9.0 : 0.36.1 ..

Usage

• For example, here is a Grafana request data.

{
  "panelId":1,
  "range":{"from":"2016-09-02T13:32:09.981Z","to":"2016-09-02T14:17:34.306Z"},
  "rangeRaw":{"from":"2016-09-02T13:32:09.981Z","to":"2016-09-02T14:17:34.306Z"},
  "interval":"2s",
  "targets":[{"target":"cpu","refId":"A"},{"target":"mem","refId":"B"}],
  "format":"json",
  "maxDataPoints":1299
}

Parse in Functional way

• Just call 'Jq#[]` with query path.

require "jq"

jq = Jq.new(str)
jq[".range.from"].as_s       # => "2016-09-02T13:32:09.981Z"
jq[".targets[].target"].as_a # => ["cpu","mem"]
jq[".format"].as_s           # => "json"
jq[".maxDataPoints"].as_i    # => 1299
jq[".xxx"]                   # Jq::NotFound("`.xxx' Missing hash key: "xxx")
jq[".xxx"]?                  # => nil

• See spec/fixtures/* files for further usage, or try crystal spec -v for full features

Auto parsing and casting by mapping

• looks like JSON.mapping except this requires Tuple(type, json_path) for its arg.
• NOTE: use Int64 rather than Int32 for Integer

require "jq"

class Request
  Jq.mapping({
    from:    {Time, ".range.from"},
    targets: {Array(String), ".targets[].target"},
    format:  String,
    max:     {Int64, ".maxDataPoints"},
  })
end

req = Request.from_json(str)
req.from        # => Time.new(2016,9,2,13,32,9,981)
req.targets     # => ["cpu","mem"]
req.format      # => "json"
req.max         # => 1299
req.to_h["max"] # => 1299

req = Request.from_json("{}")
req.max         # Jq::NotFound(key: "max")
req.max?        # => nil

default value

• override default_XXX to customize the behaviour of missing XXX

require "jq"

class User
  Jq.mapping({
    name: String,
  })

  def default_name
    "(no name)"
  end
end

user = User.from_json("{}")
user.name    # => "(no name)"

custom builder

• override build_XXX(jq : Jq, hint : String) to customize the behaviour of building XXX

Imagine a strange API that returns a String if null, regardless of the value of Int type.

[
  {"id": 1, "value": 10},
  {"id": 2, "value": "--"}
]

In this case, you can write your own logic to accept it by overriding build_count.

class Report
  Jq.mapping({
    id: Int32,
    count: Int32?,
  })

  def build_count(jq : Jq, hint : String)
    case jq.raw
    when "--"
      nil
    else
      jq.cast(Int32, hint)
    end
  end
end

reports = Array(Report).from_json <<-EOF
  [
    {"id": 1, "count": 10},
    {"id": 2, "count": "--"}
  ]
  EOF
reports.map(&.count?) # => [10, nil]

Installation

Add this to your application's shard.yml:

dependencies:
  jq:
    github: maiha/jq.cr
    version: 0.8.0

Development

cd jq.cr
crystal deps   # install dependencies
crystal spec   # run specs

Contributing

1. Fork it ( https://github.com/maiha/jq.cr/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request