A controller to handle an uploaded file and pass it to ActiveStorage correctly.

rails controller to handle file uploads.rb

def create
  #If you set up your frontend request properly, params[:avatar] will be an UploadedFile instance, which is what we want
  user = User.new(name: params[:name], avatar: params[:avatar]) 
  #passing the file in to the constructor causes ActiveStorage to attach the file automatically.
  if user.save
    puts "The user saved successfully"
    render json: user
  else
    puts "The user failed to save"
    render json: {message: "Error"}
  end
end