Graphql-ruby mutations

Mutations are graphql fields that trigger side effects.

• mutations return a hash, that contains all of the fields defined on it.
• mutations may optionally accept arguments

Documentation

official docs

https://graphql-ruby.org/guides#mutations-guides

Basics

Set the root-mutation object on the schema

class MyGraph < GraphQL::Schema
  mutation(MutationRoot)
end

Add your mutations as fields on the mutation-root
(field args set on mutation object)

class MutationRoot < GraphQL::Schema::Object
  field :write_file,
    mutation: Mutations::WriteFile
end

Define your mutation

require 'graphql'
require 'digest'

module Mutations
  class WriteFile < GraphQL::Schema::Mutation
    argument :path,     String, required: true
    argument :contents, String, required: true

    field :checksum,             String, null: false
    field :existed_before_write, Boolean, null: false

    def resolve(path:, contents:)
      abspath = File.expand_path(path)
      existed_before_write = File.exist?(abspath)
      write_file(abspath, contents)
      {
        checksum: file_checksum(abspath),
        existed_before_write: existed_before_write,
      }
    end

    private

    def write_file(path, contents)
      dirpath = File.dirname(path)
      Dir.mkdir(dirpath) unless Dir.exist?(dirpath)

      File.open(path, "w") do |fd|
        fd.write(contents)
      end
    end

    def file_checksum(path)
      File.open(path, "r") do |fd|
        Digest::MD5.hexdigest(fd.read)
      end
    end
  end
end

Now you can execute your mutation.
(note that fields converted from snake_case to camelCase).

mutation {
  writeFile(path: "~/foo.txt", contents: "boo!") {
    checksum
    existedBeforeWrite
  }
}