Example for JSON Schema in Rails?

[Oliver Kuhn]

Hi,

is out there any example, how to use JSON Schema in Rails? Cant find anything. 

Interesting for me: 

- Where to store SchemaFiles

- how to call / and load schema fieles

- do i need a helper or not...

thx in advance

[Jonas Peschla]

Hi Oliver,

I am not aware of a guide or best practices.
In our project we use json-schema to validate the payload submitted to our JSON API.
We have a base class for all API controllers which provides a parse_json and a validate_json method for guess what:

    def parse_json
      begin
        @json_data = JSON.parse(request.body.string)
      rescue
        render json: {errors: ["Unable to parse JSON: #{request.body.string}"]}.to_json, status: 400
      end
    end

    def validate_json
      errors = JSON::Validator.fully_validate(schema, @json_data, {clear_cache: false})
      if !errors.empty?
        logger.info "External API JSON Validation Error: #{errors}, #{@json_data}"
        render json: {errors: errors}.to_json, status: 422
      end
    end

The controllers inheriting from the base controller use a before_action callback to indicate when to parse and validate:
before_action :parse_json, :validate_json, only: [:create]
For validate_json to work, each controller must override/define  a schema method which returns the schema to be used for validation.

And then we have an initializer in config/initializers/json_schema.rb which uses locally cached schemas instead of fetching them (plus to register custom validators):
JSON_SCHEMAS = Dir.glob('lib/assets/schemas/*.json').reduce({}) do |memo, path|
  schema = path.match(/\/([^\/\s]+)\.schema\.json\z/)[1]
  memo.tap { |m| m[schema] = File.read(path) }
end

class CustomSchemaReader < JSON::Schema::Reader
  def read_uri(uri)
    schema = uri.path.match(/www\.example\.com\/([^\/\s]+)\z/)[1]
    JSON_SCHEMAS[schema]
  end
end

JSON::Validator.schema_reader = CustomSchemaReader.new(:accept_uri => true, :accept_file => !Rails.env.production?)

For us this works. If you are looking for using json-schema as a validator for serialized hashes in ActiveModel attributes you might be
interested in Iains gem for that: https://github.com/iainbeeston/json_validator

Regards
Jonas

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[Oliver Kuhn]

Thank you so much. Seems to solve my problem. i will try This in the next days.

[Oliver Kuhn]

Only to give a status: i am using https://github.com/iainbeeston/json_validator for now... its very simple and all i need... thank you for this hint.

[Iain Beeston]

I'm glad you find it useful. Please let me know (via github issues) if you have any feedback or suggestions to improve it.

[jenna....@gmail.com]

Thanks! This was useful for me too!