Ruby on Rails + Active_Record: How do I include child counts in result?

I figured out how to include the children in a to_json result by creating an as_json method in the folder model.

def as_json(options={ })
  super(
          options.merge(
                  :include => {
                          :children => { }
                  }
          )
  )
end

The above code gives me a list of the children, but what I want is to include the count not the list of children. I also want to filter it to only "Active" children.

I can't seem to figure out an efficient way to do this.

I'm开发者_开发问答 using the below code to return a list of folders.

def index
  @folders = Folder.all(:order => "Name")

  respond_with(@folders) do |format|
    format.jsonp { render :json => @folders, :callback => params[:callback] }
  end
end

Finally, I want to make sure the count comes back in all results not just json. json is the most important but I do want to make sure it's in the others as well.

I thought I would be able to add the count to each of the folders returned by @folders after the query by using .size. However, that doesn't seem to work...

Next I started looking into adding a method to the Folder model such as...

def child_count
  write_attribute(:child_count, children.size)
end

But after looking at it I realized that's not really going to work...

So now I'm looking into :select to do some sql magic... but I really don't want to go that route if there's a cleaner way.

Tips appreciated!

Just add a child_count method that returns the number of children and then use the :methods option for as_json:

def as_json(options = { })
    super(options.merge(:methods => :child_count))
end

You might want to be a bit more careful with that merge though, if there is a :methods already in options you'll overwrite it; something like this might serve you better than a straight merge:

def add_child_count(options)
    options[:methods] = [ options[:methods], :child_count ].flatten.compact.uniq
    options
end

def as_json(options = { })
    super(add_child_count(options))
end

For XML, you do pretty much the same thing with to_xml instead of as_json.