create_movie.rb

# app/graphql/resolvers/create_movie.rb

class Resolvers::CreateMovie < GraphQL::Function
  # arguments passed as "args"
  argument :name,   !types.String
  argument :year,   types.String
  argument :genre,  types.String

  # return type from the mutation
  type Types::MovieType

  # the mutation method
  def call(_obj, args, _ctx)
    movie_params  = { name: args[:name], year: args[:year], genre: args[:genre] }
    movie         = Movie.new(movie_params)
    movie.save!

    ActionCable.server.broadcast(
      'movies',
      name:   movie.name,
      year:   movie.year,
      genre:  movie.genre
    )

    movie
  end
end