Creating a custom Rails generator

For the purpose of this tutorial, assume we're making a custom generator named gqlspec.

Run rails g generate gqlspec. It should generate the following files and folders.

• lib/generators
• lib/generators/gqlspec
• lib/generators/gqlspec/templates
• lib/generators/gqlspec/gqlspec_generator.rb
• lib/generators/gqlspec/USAGE

Edit your USAGE file with the appropriate data. The data in this file will be shown whenever you run rails g gqlspec --help

// lib/generators/gqlspec/USAGE

Description:
    Setups up rspec for a GraphQL mutation.

Example:
    rails generate gqlspec mutation_name

    This will create:
        spec/graphql/mutations/mutation_name_spec.rb

In your lib/generators/gqlspec/gqlspec_generator.rb file

• Change Rails::Generators::NamedBase to Rails::Generators::Base. Inheriting from NamedBase with automatically define a name argument with its value set to your custom generator's name.
• Define the arguments for your generator.

argument :mutation, type: :string, required: true, default: "", description: ""

• Optionally, define options for your generator. You can access an option's arguments with options[:arguments]

class_option :arguments, type: :array, required: true, default: []

• Define templates for use as a base when generating files.
  • You can copy the exact contents of a template to a different location using the copy_file method
  • You can copy the contents of a template after it has been run through Rails' template engine to a different location using the template method

# lib/generators/gqlspec/templates/mutation_spec.template
require "rails_helper"

module Mutations
    RSpec.describe <%= mutation.camelize %>, type: :request do
        describe "resolve" do
        end

        def data(response, key)
            gql_response(response, mutation.camelize(:lower))[key.to_s]
        end

        def query(<%= "#{arguments.join(", ")}" %>)
            <<~GQL
                mutation{
                    <%= mutation.camelize(:lower) %>(input: {<%= "#{arguments.map{|argument| "#{argument}: \"\#{#{argument}}\"" }.join(", ")}" %>}){
                        status, data, errors
                    }
                }
            GQL
        end
    end
end

Important to note

• Any public methods in your generator class will automatically be called in the order they were defined. If you don't want a method to be called, mark it as private.
• Methods defined in your generator class will be available for use in your template.

Here's what your generator class should look like in the end:

# lib/generators/gqlspec/gqlspec_generator.rb
class GqlSpecGenerator < Rails::Generators::Base
    source_root File.expand_path("templates", __dir__)
    argument :mutation, type: :string, required: true
    class_option :arguments, type: :array, required: true, default: []

    def generate_mutation
        generate_spec_file
    end

    private

    def generate_spec_file
        template "mutation_spec.template", "spec/graphql/mutations/#{mutation}_spec.rb"
    end

    def arguments
        options[:arguments]
    end
end

Here's what using it will look like:

• Run rails g gqlspec forgot_password --arguments email
• If you followed this tutorial correctly, our gqlspec generator should generate the file below:

# app/graphql/mutations/forgot_password_spec.rb
require "rails_helper"

module Mutations
    RSpec.describe ForgotPassword, type: :request do
        describe "resolve"
        end

        def data(response, key)
            gql_response(response, "forgotPassword")[key.to_s]
        end

        def query(email)
            <<~GQL
                mutation{
                    forgotPassword(input: {email: "#{email}"}){
                        status, data, errors
                    }
                }
            GQL
        end
    end
end