JSON Table Schema

A utility library for working with JSON Table Schema in Ruby.

Installation

Add this line to your application's Gemfile:

gem 'jsontableschema'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jsontableschema

Usage

Parse a CSV

Validate and cast data from a CSV as described by a schema.

schema = {
    "fields": [
        {
            "name" => "id",
            "title" => "Identifier",
            "type" => "integer"
        },
        {
            "name" => "title",
            "title" => "Title",
            "type" => "string"
        }
    ]
} # Can also be a URL or a path

csv = 'https://github.com/theodi/jsontableschema.rb/raw/master/spec/fixtures/simple_data.csv' # Can also be a url or array of arrays

table = JsonTableSchema::Table.new(csv, schema)
table.rows
#=> [[1,'foo'],[2,'bar'],[3,'baz']]

Infer a schema

If you don't have a schema for a CSV, and want to generate one, you can infer a schema like so:

csv = 'https://github.com/theodi/jsontableschema.rb/raw/master/spec/fixtures/simple_data.csv' # Can also be a url or array of arrays

table = JsonTableSchema::Table.infer_schema(csv)
table.schema
#=> {"fields"=>[{"name"=>"id", "title"=>"", "description"=>"", "type"=>"string", "format"=>"default"}, {"name"=>"title", "title"=>"", "description"=>"", "type"=>"string", "format"=>"default"}]}

Validate a schema

To validate that a schema meets the JSON Table Schema spec, you can pass a schema to the initializer like so:

schema_hash = {
  "fields" => [
      {
          "name" => "id"
      },
      {
          "name" => "height"
      }
  ]
}

schema = JsonTableSchema::Schema.new(schema_hash)
schema.valid?
#=> true

You can also pass a file path or URL to the initializer:

schema = JsonTableSchema::Schema.new('http://example.org/schema.json')
schema.valid?
#=> true

If the schema is invalid, you can access the errors via the messages attribute

schema_hash = {
  "fields" => [
    {
      "name"=>"id",
      "title"=>"Identifier",
      "type"=>"integer"
   },
   {
     "name"=>"title",
     "title"=>"Title",
     "type"=>"string"
    }
  ],
 "primaryKey"=>"identifier"
}

schema.valid?
#=> false
schema.messages
#=> ["The JSON Table Schema primaryKey value `identifier` is not found in any of the schema's field names"]

Schema Model

You can also access the schema via a Ruby model, with some useful methods for interaction:

schema_hash = {
  "fields" => [
      {
          "name" => "id",
          "type" => "string",
          "constraints" => {
            "required" => true,
          }
      },
      {
          "name" => "height",
          "type" => "number"
      }
  ],
  "primaryKey" => "id",
  "foreignKeys" => [
    {
        "fields" => "state",
        "reference" => {
            "datapackage" => "http://data.okfn.org/data/mydatapackage/",
            "resource" => "the-resource",
            "fields" => "state_id"
        }
    }
  ]
}

schema = JsonTableSchema::Schema.new(schema_hash)

schema.headers
#=> ["id", "height"]
schema.required_headers
#=> ["id"]
schema.fields
#=> [{"name"=>"id", "constraints"=>{"required"=>true}, "type"=>"string", "format"=>"default"}, {"name"=>"height", "type"=>"number", "format"=>"default"}]
schema.primary_keys
#=> ["id"]
schema.foreign_keys
#=> [{"fields" => "state", "reference" => { "datapackage" => "http://data.okfn.org/data/mydatapackage/", "resource" => "the-resource", "fields" => "state_id" } } ]
schema.get_field('id')
#=> {"name"=>"id", "constraints"=>{"required"=>true}, "type"=>"string", "format"=>"default"}
schema.has_field?('foo')
#=> false
schema.get_type('id')
#=> 'string'
schema.get_fields_by_type('string')
#=> [{"name"=>"id", "constraints"=>{"required"=>true}, "type"=>"string", "format"=>"default"}, {"name"=>"height", "type"=>"string", "format"=>"default"}]
schema.get_constraints('id')
#=> {"required" => true}
schema.cast_row(['string', '10.0'])
#=> ['string', 10.0]
schema.cast([['foo', '12.0'],['bar', '10.0']])
#=> [['foo', 12.0],['bar', 10.0]]

When casting a row (using cast_row), or a number of rows (using cast), by default the converter will fail on the first error it finds. If you pass false as the second argument, the errors will be collected into a errors attribute for you to review later. For example:

schema_hash = {
  "fields" => [
      {
          "name" => "id",
          "type" => "string",
          "constraints" => {
            "required" => true,
          }
      },
      {
          "name" => "height",
          "type" => "number"
      }
  ]
}

schema = JsonTableSchema::Schema.new(schema_hash)

rows = [
  ['foo', 'notanumber'],
  ['bar', 'notanumber'],
  ['wrong column count']
]

schema.cast(rows)
#=> JsonTableSchema::InvalidCast: notanumber is not a number
schema.cast(rows, false)
#=> JsonTableSchema::MultipleInvalid
schema.errors
#=> [#<JsonTableSchema::InvalidCast: notanumber is not a number>, #<JsonTableSchema::InvalidCast: notanumber is not a number>, #<JsonTableSchema::ConversionError: The number of items to convert (1) does not match the number of headers in the schema (2)>]

Field

# Init field
field = JsonTableSchema::Field.new({'type': 'number'})

# Cast a value
field.cast_value('12345')
#=> 12345.0

Data values can be cast to native Ruby objects with a Field instance. Type instances can be initialized with field descriptors. This allows formats and constraints to be defined.

Casting a value will check the value is of the expected type, is in the correct format, and complies with any constraints imposed by a schema. E.g. a date value (in ISO 8601 format) can be cast with a DateType instance. Values that can't be cast will raise an InvalidCast exception.

Casting a value that doesn't meet the constraints will raise a ConstraintError exception.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/jsontableschema. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.