Schemable

The Schemable gem provides a simple way to define a schema for a Rails model in JSONAPI format. It can automatically generate a schema for a model based on the model's attributes. It is also highly customizable, allowing you to modify the schema to your liking by overriding configuration options and methods.

This gem is preferably to be used with RSwag gem to generate the swagger documentation for your API.

Installation

Add this line to your application's Gemfile:

gem 'schemable'

And then execute:

bundle install

Or install it yourself as:

gem install schemable

Usage

The installation command above will install the Schemable gem and its dependencies. However, in order for Schemable to work, you must also implement your own logic to use the generated schemas to feed it to RSwag.

The below command is to initialize the gem and generate the configuration file.

rails g schemable:install

This will generate schemable.rb in your config/initializers directory. This file will contain the configuration for the Schemable gem. You can modify the configuration to your liking. For more information on the configuration options, see the Configuration section below.

Generating Definition Files

The Schemable gem provides a generator that can be used to generate definition files for your models. To generate a definition file for a model, run the following command:

rails g schemable:model --model_name <model_name>

This will generate a definition file for the specified model in the lib/swagger/definitions directory. The definition file will be named <model_name>.rb. This file will have the bare minimum code required to generate a schema for the model. You can then modify the definition file to your liking by overriding the default methods. For example, you can add or remove attributes from the schema, or you can add or remove relationships from the schema. You can also add custom attributes to the schema. For more information on how to customize the schema, see the Customizing the Schema section below.

Configuration

The Schemable gem provides a number of configuration options that can be used to customize the behavior of the gem. The following is a list of the configuration options that are available.

Please note that the configurations options below are defined in the Schemable module of the gem. To configure the gem, simply override the default values in the config/initializers/schemable.rb file. Also the changes will affect all the definition classes globally.

---

Option Name	Description	Default Value
orm	The ORM that is used in the application. The options are :active_record and :mongoid.	true
float_as_string	Whether or not to convert the float type to a string type in the schema.	false
decimal_as_string	Whether or not to convert the decimal type to a string type in the schema.	false
custom_type_mappers	A hash of custom type mappers that can be used to override the default type mappers. A specific method should be used, see Annex 1.0 - Add custom type mapper for more information.	{}
use_serialized_instance	Whether or not to use the serialized instance in the process of schema generation as type fallback for virtual attributes. See Annex 1.1 - Use serialized instance for more information.	false
custom_defined_enum_method	The name of the method that is used to get the enum keys and values. This allows applications with the orm mongoid define a method that mimicks what defined_enums does in activerecord. Please see Annex 1.2 - Custom defined enum method for an example.	nil
enum_prefix_for_simple_enum	The prefix to be used for the enum values when mongoid is used.	nil
enum_suffix_for_simple_enum	The suffix to be used for the enum values when mongoid is used.	nil
infer_attributes_from_custom_method	The name of the custom method that is used to get the attributes to be generated in the schema. See Annex 1.3 - Infer attributes from custom method for more information.	nil
infer_expand_nested_from_expand	Configures ResponseSchemaGenerator's generate method to prevent expansion for nested relationships. It globally set the value of expand_nested to the same value as expand by setting the configuration to true	flase
infer_attributes_from_jsonapi_serializable	Whether or not to infer the attributes from the JSONAPI::Serializable::Resource class. See the previous example Annex 1.1 - Use serialized instance for more information.	false
custom_meta_response_schema	A hash of custom meta response schema that can be used to override the default meta response schema. See Annex 1.4 - Custom meta response schema for more information.	nil
pagination_enabled	Enable pagination schema generation in the meta section of the response schema.	true

---

Customizing the Schema

The Schemable gem provides a number of methods that can be used to customize the schema. These methods are defined in the Schemable::Definition class of the gem. To customize the schema for a specific model, simply override the default methods in the Schemable::Definition class for the model.

Please read the method inline documentation before overriding to avoid any unexpected behavior.

The following is a list of the methods that can be overridden. (See the example in Annex 1.5 - Highly Customized Definition for a highly customized definition file.)

---

Method Name	Description
serializer	Returns the serializer of the model for the definition.
attributes	Returns the attributes for the definition based on the configuration.
relationships	Returns the relationships defined in the model.
array_types	Returns a hash of all the arrays defined for the model.
optional_create_request_attributes	Returns the attributes that are not required in the create request.
optional_update_request_attributes	Returns the attributes that are not required in the update request.
nullable_attributes	Returns the attributes that are nullable in the request/response body.
nullable_relationships	Returns the relationships that are nullable in the response body.
additional_create_request_attributes	Returns the additional create request attributes that are not automatically generated.
additional_update_request_attributes	Returns the additional update request attributes that are not automatically generated.
additional_response_attributes	Returns the additional response attributes that are not automatically generated.
additional_response_relations	Returns the additional response relations that are not automatically generated.
additional_response_included	Returns the additional response included that are not automatically generated.
excluded_create_request_attributes	Returns the attributes that are excluded from the create request schema.
excluded_update_request_attributes	Returns the attributes that are excluded from the update request schema.
default_value_for_enum_attributes	Returns the default value for the enum attributes. Used when you want a custom value for the default enum. By default the first key is used as default
excluded_response_attributes	Returns the attributes that are excluded from the response schema.
excluded_response_relations	Returns the relationships that are excluded from the response schema.
excluded_response_included	Returns the included that are excluded from the response schema.
serialized_instance	Returns an instance of the model class that is already serialized into jsonapi format.
model	Returns the model class (Constantized from the definition class name).
model_name	Returns the model name. Used for schema type naming.
camelize_keys	Given a hash, it returns a new hash with all the keys camelized.
generate	Returns the schema for the create request body, update request body, and response body.

---

Examples

The followings are some examples of configuration of the gem to have different behaviors based on the application needs. In the above section, we have already seen how to generate the definition files for the models. The following examples will show how to customize the schema for the models. Also, we will see how to use the generated schema in RSwag to generate the swagger documentation for the API.

Annex 1.0 - Add custom type mapper

# config/initializers/schemable.rb

Schemable.configure do |config|
  config.add_custom_type_mapper(
    :string,
    { type: :text }
  )
end

Annex 1.1 - Use serialized instance

# config/initializers/schemable.rb

Schemable.configure do |config|
  config.use_serialized_instance = true
end

Then in the definition file, you can override the serialized_instance method to return the serialized instance of the model. Let's also assume that we want to use the JSONAPI::Serializable::Resource class to serialize the instance.

# lib/swagger/definitions/user_application.rb

module Swagger
  module Definitions
    class User < Schemable::Definition
      attr_accessor :instance

      def serializer
        V1::UserSerializer
      end

      def serialized_instance
        @instance ||= JSONAPI::Serializable::Renderer.new.render(
          FactoryBot.create(:user),
          class: { User: serializer },
          include: []
        )
      end
    end
  end
end

Annex 1.2 - Custom defined enum method

Let's assume that we also want to use mongoid in our application. In this case, we need to define a method that mimicks what defined_enums does in activerecord. Let's assume that we have a model called User that has an enum field called status. The following is an example of how to define the method:

# app/models/user.rb

class User < ApplicationModel
  include Mongoid::Document
  include SimpleEnum::Mongoid

  as_enum :status, active: 0, inactive: 1
end

Then in the ApplicationModel class, we can define the method as follows:

# app/models/application_model.rb

def self.custom_defined_enum(suffix: '_cd', prefix: nil)
  defined_enums = {}
  enum_fields = if prefix
                  fields.select { |k, v| k.to_s.start_with?(prefix) }
                else
                  fields.select { |k, v| k.to_s.end_with?(suffix) }
                end

  enum_fields.each do |k, v|
    enum_name = k.to_s.gsub(prefix || suffix, '')
    enum = send(enum_name.pluralize)

    defined_enums[enum_name] = enum.hash
  end

  defined_enums
end

This method will work for all the models that have enum fields. Since Simple Enum gem defines enum fields with the suffix _cd, we can use the suffix option to get the enum fields. However, if the enum fields are defined with a different suffix, we can use the prefix option to get the enum fields.

Now, we need to specify theses options in the configuration file:

# config/initializers/schemable.rb

Schemable.configure do |config|
  config.custom_defined_enum_method = :custom_defined_enum
  config.enum_suffix_for_simple_enum = '_cd'
end

This will generate the schema for the enum fields in the model as follows:

{
  # ...
    status: {
      type: string,
      enum: ['active', 'inactive']
    }
  # ...
}

Annex 1.3 - Infer attributes from custom method

Sometimes, we may want to infer the attributes from a custom method. For example, let's assume that we have a model called User that has a method called base_attributes that returns an array of attributes. The following is an example of how to define the method:

# app/models/user.rb

class User < ApplicationModel
  def self.base_attributes
    %i[
      id
      name
      email
      status
      roles
      created_at
      updated_at
    ]
  end
end

Then in the configuration file, we can override the infer_attributes_from_custom_method method to return the attributes from the custom method:

# config/initializers/schemable.rb

Schemable.configure do |config|
  config.infer_attributes_from_custom_method = :base_attributes
end

if we want to use the base_attributes method for only the User model, we can override the attributes method in the Schemable::Definition class as follows:

# lib/swagger/definitions/user.rb

module Swagger
  module Definitions
    class User < Schemable::Definition
      def attributes
        model.base_attributes
      end
    end
  end
end

Annex 1.4 - Custom meta response schema

Sometimes, we may want to customize the meta response schema. For example, let's assume that we want to add a total attribute to the meta response schema. The following is an example of how to do that:

# config/initializers/schemable.rb

Schemable.configure do |config|
  config.custom_meta_response_schema = {
    type: :object,
    properties: {
      total: { type: :integer }
    }
  }
end

Annex 1.5 - Highly Customized Definition

The below is a definition file for a model that has been customized in a way that many of the methods have been overridden. This is just an example of how to customize the schema. You can customize the schema to your liking. The below hypothetical model's logic does not matter. The only thing that matters is the schema customization and being familiar with the methods that can be overridden.

Click to expand

module Swagger
  module Definitions
    class Order < Schemable::Definition
      def relationships
        @relationships ||= {
          belongs_to: {
            address: Swagger::Definitions::Address.new
          },
          has_many: {
            items: Swagger::Definitions::Item.new
          },
          addition_to_included: {
            store: Swagger::Definitions::Store.new,
            attachments: Swagger::Definitions::Upload.new
          }
        }
      end

      def excluded_create_request_attributes
        create_params = model.create_params.select { |item| item.is_a?(Symbol) }
        model.base_attributes + %i[comment applicable_transitions] - create_params
      end

      def excluded_update_request_attributes
        update_params = model.update_params.select { |item| item.is_a?(Symbol) }
        model.base_attributes + %i[comment applicable_transitions] - update_params
      end

      def additional_create_request_attributes
        @additional_create_request_attributes ||= {
          items_attributes:
            {
              type: :array,
              items: {
                anyOf: [
                  {
                    type: :object,
                    properties: Schemable::RequestSchemaGenerator.new(Swagger::Definitions::Item.new).generate_for_create.as_json['properties']['data']['properties']
                  }
                ]
              }
            }
        }
      end

      def additional_update_request_attributes
        @additional_update_request_attributes ||={
          items_attributes:
            {
              type: :array,
              items: {
                anyOf: [
                  {
                    type: :object,
                    properties:Schemable::RequestSchemaGenerator.new(Swagger::Definitions::Item.new).generate_for_update.as_json['properties']['data']['properties']
                  }
                ]
              }
            }
        }
      end

      def additional_response_attributes
        {
          comment: { type: :object, properties: {}, nullable: true },
          item_status: { type: :string, nullable: true },
          applicable_transitions: {
            type: :array,
            items:
              {
                type: :object, nullable: true,
                properties:
                  {
                    name: { type: :string, nullable: true },
                    metadata: { type: :object, nullable: true }
                  }
              },
            nullable: true
          }
        }
      end

      def nullable_attributes
        %i[contact_number email]
      end

      def optional_create_request_attributes
        %i[contact_number email]
      end

      def optional_update_request_attributes
        %i[contact_number email]
      end

      def self.generate
        schema_instance = new

        [
          "#{schema_instance.model}CreateRequest": schema_instance.camelize_keys(Schemable::RequestSchemaGenerator.new(schema_instance).generate_for_create),
          "#{schema_instance.model}UpdateRequest": schema_instance.camelize_keys(Schemable::RequestSchemaGenerator.new(schema_instance).generate_for_update),
          "#{schema_instance.model}Response": schema_instance.camelize_keys(Schemable::ResponseSchemaGenerator.new(schema_instance).generate(expand: true, collection: true, relationships_to_exclude_from_expansion: %w[addresses stores attachments])),
          "#{schema_instance.model}ResponseExpanded": schema_instance.camelize_keys(Schemable::ResponseSchemaGenerator.new(schema_instance).generate(expand: true, expand_nested: true))
        ]
      end
    end
  end
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/schemable. This project is intended to be a safe, welcoming space for collaboration, and contributors. Please go to issues page to report any bugs or feature requests. If you would like to contribute, please fork the repository and submit a pull request.

To, use the gem locally, clone the repository and run bundle install to install dependencies. Then, run bundle exec rspec to run the tests.

License

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