error_messages_for does not display the error

rubyonrails-talk
1

Hi all

I've approached Rails since a couple of months to develop a quick application for my company. Fantastic framework. As every noob, I do have some gaps to cover. The one which is giving me a little frustration, generated by my lack of knowledge is as follows.

I need to make sure the region object is not deleted if there are countries associated with it. I solved this by putting a before_destroy methon in the model, as follows:

class Region < ActiveRecord::Base   has_many :countries

  validates_presence_of :name   validates_uniqueness_of :name

  def before_destroy     unless countries.count == 0       errors.add_to_base "Cannot delete a region with countries associated"       return false     end   end end

This prevents the deletion if countries are associated to it. By adding the error to the errors collection of the region object, I expected to receive a message on the page by adding the follwing in the application layout

---cut--- <%= error_messages_for :region %> <%= yield :layout %> ---cut---

actually the error_messages_for is much longer as it lists all the objects. The tag works for input forms, but in this specific scenario no error message is displayed.

The error is however populated, I verified it with the logger.info in the various steps.

After crushing my head trying to figure out why, I gave up the old way, finding another solution. But I do not like it because ruby and rails are very elegant in their syntax. Here is what I did: in the controller I modified the destroy method like this

  def destroy     @region = Region.find(params[:id])     @region.destroy

    @region.errors.each_full{|msg| flash[:error] = msg } unless @region.errors.count == 0

    respond_to do |format|       format.html { redirect_to(regions_url) }       format.xml { head :ok }     end   end

I know, it's an horror, I can name many resons why including the fact that only the last error is displayed, but could not figure out a better way. I'm pretty sure that the solution is right in front of me but cannot find it....

Any suggestion very welcome.

Thanks

2

This might help you out...

http://api.rubyonrails.org/classes/ActionController/Flash.html

Although it's not immediately apparent from the rdocs, you can flash [:error] in addition to the documented flash[:notify] - think of them as "alerts" and "alarms". If you carry the error/notify distinction into the erb with:

     <% if flash[:notice] %>        <div class="notice"><%= flash[:notice] %></div>      <% end %>       <% if flash[:error] %>        <div class="error"><%= flash[:error] %></div>      <% end %>

you can use the class to provide css color decoration (notice <=> yellow, error <=> red)

Just be aware that the flash is a temporary buffer - the text is volatile by default - and refreshing the window will erase the message.

3

To extend on that, flash is just a hash (which happens to be stored in the session and which rails clears out appropriately) - you can store anything you want in it, for any key you want.

Fred

4

Hi all

I found the solution to my problems...

My mistake (of course because of ignorance) was to look in the wrong place. The error populated in the model.errors hash are rendered by the error_messages_for method only if the render method in the ActionController is invoked.

Therefore the code should look like this.

The model:

class Region < ActiveRecord::Base   has_many :countries

  validates_presence_of :name   validates_uniqueness_of :name

  def before_destroy     unless countries.count == 0       errors.add_to_base "Cannot delete a region with countries associated"       return false     end   end end

The method destroy in the controller

  def destroy     @region = Region.find(params[:id])

    respond_to do |format|       if @region.destroy         format.html { redirect_to(regions_url) }         format.xml { head :ok }       else         format.html { render :action => "show" }         format.xml { render :xml => @region.errors, :status => :unprocessable_entity }       end     end   end

Et voilà, here is the error displayed on screen...

Steve