#forgive me, this just isn't clear to me (yet)...

# here is [part of] my project's SHOW view:


<% form_for @image, :html => { :multipart => true } do |f| %>
  

    Upload Image

    <%= f.file_field :image_file %>

    or URL: <%= f.text_field :image_file_url %>
    <%- if @image.new_record? -%>
      <%= f.hidden_field :project_id %>
    <%- end -%>
  
  

    <%= f.submit "Upload Image" %>
  
<% end %>

#  here is the project controller's show action:

  def show
    @project = Project.find(params[:id])
    @image = @project.images.build
    if params[:image_id]
      @myimage = @project.images.find_by_id(params[:image_id])
    end

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @project }
    end
  end

#  here is the Image controller's create action:

  def create
    @project = Project.find(params[:project_id])
    @image = @project.images.build(params[:image])
    if @image.save
      redirect_to image_url(@image)
    else
      flash[:notice] = 'Your image did not pass validation!'
      render :action => 'new'
    end
  end