Why do I get this noMethodError error?

This is the error:

NoMethodError in VideosController#update

undefined method `each' for #<Topic:0x1032ee开发者_如何学编程330>

This is the application trace:

app/models/video.rb:19:in `assign_topics'
app/controllers/videos_controller.rb:41:in `update'
app/controllers/videos_controller.rb:40:in `update'

this is my assign_topics method:

def assign_topics
  if @topic_names
    self.topics = Topic.find_or_create_by_name(@topic_names)
  end
end

Note that I'm following this: http://media.railscasts.com/videos/167_more_on_virtual_attributes.mov

Here's the video controller's update method:

def update
    @video = current_user.videos.find(params[:id])

    respond_to do |format|
      if @video.update_attributes(params[:video])
        format.html { redirect_to(@video, :notice => 'Video was successfully updated.') }
      else
        format.html { render :action => "edit" }
      end
    end
  end

I'd guess that your assign_topics method is at fault. Topic.find_or_create_by_name will return a single Topic instance, then you assign that to self.topics and self.topics is probably expecting an Array (or some other Enumerble); then later, the update process will try to loop through self.topics using each and you get your error.

You mention, in a comment, that you tried something like this:

self.topics = @topic_names.each { |n| Topic.find_or_create_by_name(n) }

But that won't work because each returns the original array and so the above is equivalent to this:

@topic_names.each { |n| Topic.find_or_create_by_name(n) }
self.topics = @topic_names

and all the Topic instances that you found/created are simply thrown away.

So, you might have better luck using collect like this:

def assign_topics
    if @topic_names
        self.topics = @topic_names.collect { |n| Topic.find_or_create_by_name(n) }
    end
end

You are getting a NoMethodError Exception because somewhere in your code you are trying to loop, via .each(), on something that is not an array/enumerable.

According to your exception, you are calling .each() on a Model Object(Topic), which would make sense to not have the .each() method.