This library is intended to provide Ruby with an interface for validating JSON objects against a JSON schema conforming to JSON Schema Draft 3. Legacy support for JSON Schema Draft 2 and JSON Schema Draft 1 is also included.
The JSON::Schema library has no dependencies if the validation methods are called using Ruby objects. However, either the json
or the yajl-ruby
gem needs to be installed to validate JSON strings or files containing JSON data.
From rubygems.org:
gem install json-schema
From the git repo:
$ gem build json-schema.gemspec $ gem install json-schema-1.1.1.gem
Three base validation methods exist: validate
, validate!
, and fully_validate
. The first returns a boolean on whether a validation attempt passes and the second will throw a JSON::Schema::ValidationError
with an appropriate message/trace on where the validation failed. The third validation method does not immediately fail upon a validation error and instead builds an array of validation errors return when validation is complete.
All methods take two arguments, which can be either a JSON string, a file containing JSON, or a Ruby object representing JSON data. The first argument to these methods is always the schema, the second is always the data to validate. An optional third options argument is also accepted; available options are used in the examples below.
By default, the validator uses the JSON Schema Draft 3 specification for validation; however, the user is free to specify additional specifications or extend existing ones. Legacy support for Draft 1 and Draft 2 is included by either passing an optional :version
parameter to the validate
method (set either as :draft1
or draft2
), or by declaring the $schema
attribute in the schema and referencing the appropriate specification URI. Note that the $schema
attribute takes precedence over the :version
option during parsing and validation.
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "required" => true} } } data = { "a" => 5 } JSON::Validator.validate(schema, data)
require 'rubygems' require 'json-schema' JSON::Validator.validate('schema.json', '{"a" : 5}')
require 'rubygems' require 'json-schema' data = ['user','user','user'] JSON::Validator.validate('user.json', data, :list => true)
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "required" => true} } } data = { "a" => "taco" } begin JSON::Validator.validate!(schema, data) rescue JSON::Schema::ValidationError puts $!.message end
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "required" => true}, "b" => {"type" => "string", "required" => "true"} } } data = { "a" => "taco" } errors = JSON::Validator.fully_validate(schema, data) # ["The property '#/a' of type String did not match the following type: integer in schema 03179a21-197e-5414-9611-e9f63e8324cd#", "The property '#/' did not contain a required property of 'b' in schema 03179a21-197e-5414-9611-e9f63e8324cd#"]
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "required" => true}, "b" => {"type" => "string", "required" => "true"} } } data = { "a" => "taco" } errors = JSON::Validator.fully_validate(schema, data, :errors_as_objects => true) # [{:message=>"The property '#/a' of type String did not match the following type: integer in schema 03179a21-197e-5414-9611-e9f63e8324cd#", :schema=>#<URI::Generic:0x103a76198 URL:03179a21-197e-5414-9611-e9f63e8324cd#>, :failed_attribute=>"Type", :fragment=>"#/a"}, {:message=>"The property '#/' did not contain a required property of 'b' in schema 03179a21-197e-5414-9611-e9f63e8324cd#", :schema=>#<URI::Generic:0x103a76198 URL:03179a21-197e-5414-9611-e9f63e8324cd#>, :failed_attribute=>"Properties", :fragment=>"#/"}]
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "required" => "true"} # This will fail schema validation! } } data = { "a" => 5 } JSON::Validator.validate(schema, data, :validate_schema => true)
With the :insert_defaults option set to true any missing property that has a
default value specified in the schema will be inserted into the validated data. The inserted default value is validated hence catching a schema that specifies an invalid default value.
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "default" => 42, "required" => "true"}, "b" => {"type" => "integer"} } } # Would not normally validate because "a" is missing and required by schema, # but "default" option allows insertion of valid default. data = { "b" => 5 } JSON::Validator.validate(schema, data) # false JSON::Validator.validate(schema, data, :insert_defaults => true) # true # data = { # "a" => 42, # "b" => 5 # }
require 'rubygems' require 'json-schema' schema = { "type" => "object", "properties" => { "a" => {"type" => "integer", "optional" => true} } } data = { "a" => 5 } JSON::Validator.validate(schema, data, :version => :draft2)
For this example, we are going to extend the JSON Schema Draft 3 specification by adding a ‘bitwise-and’ property for validation.
require 'rubygems' require 'json-schema' class BitwiseAndAttribute < JSON::Schema::Attribute def self.validate(current_schema, data, fragments, processor, validator, options = {}) if data.is_a?(Integer) && data & current_schema.schema['bitwise-and'].to_i == 0 message = "The property '#{build_fragment(fragments)}' did not evaluate to true when bitwise-AND'd with #{current_schema.schema['bitwise-or']}" raise JSON::Schema::ValidationError.new(message, fragments, current_schema) end end end class ExtendedSchema < JSON::Schema::Validator def initialize super extend_schema_definition("http://json-schema.org/draft-03/schema#") @attributes["bitwise-and"] = BitwiseAndAttribute @uri = URI.parse("http://test.com/test.json") end JSON::Validator.register_validator(self.new) end schema = { "$schema" => "http://test.com/test.json", "properties" => { "a" => { "bitwise-and" => 1 }, "b" => { "type" => "string" } } } data = { "a" => 0 } data = {"a" => 1, "b" => "taco"} JSON::Validator.validate(schema,data) # => true data = {"a" => 1, "b" => 5} JSON::Validator.validate(schema,data) # => false data = {"a" => 0, "b" => "taco"} JSON::Validator.validate(schema,data) # => false
The JSON Schema library currently supports the json
and yajl-ruby
backend JSON parsers. If either of these libraries are installed, they will be automatically loaded and used to parse any JSON strings supplied by the user.
If more than one of the supported JSON backends are installed, the yajl-ruby
parser is used by default. This can be changed by issuing the following before validation:
JSON::Validator.json_backend = :json
Optionally, the JSON Schema library supports using the MultiJSON library for selecting JSON backends. If the MultiJSON library is installed, it will be autoloaded.
The following core schema attributes are not implemented:
- default – This library aims to solely be a validator and does not modify an object it is validating.
The ‘format’ attribute is only validated for the following values:
- date-time
- date
- time
- ip-address
- ipv6
All other ‘format’ attribute values are simply checked to ensure the instance value is of the correct datatype (e.g., an instance value is validated to be an integer or a float in the case of ‘utc-millisec’).
Additionally, JSON::Validator does not handle any json hyperschema attributes.