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Displaying ActiveRecord validation errors from AJAX requests

I haven’t been able to find anything built into Rails to present errors from model validation when a request is sent via AJAX.

So I came up with this handly little hack, which I’ve put in my application.rb file.

def render_javascript_alert_for_errors_on(object)
  errors = object.errors.full_messages
  alert_text = errors.collect { |error| '-' + error }.join("\n")
  render :update do |page|
    page.alert alert_text

This takes the object and displays a nicely-formatted version of all the errors on that object, taking advantage of inline RJS to render the javascript to create an alert().

It works perfectly, but it still feels a little “hacky” to me. Any better ideas?

ActiveRecord DOM IDs

The solution—or at least a nice, cheap bandaid that can be applied easily, consists of adding a method to ActiveRecord::Base to help generate these ids without any brainpower involved.

Here’s a very simple implementation that I use in my projects, courtesy of Jamis Buck:

class ActiveRecord::Base
  def dom_id(prefix=nil)
    display_id = new_record? ? "new" : id
    prefix ||=
    prefix != :bare ? "#{prefix.to_s.dasherize}-#{display_id}" : display_id
endSo, you can do stuff like this in your views:

<% @entries.each do |entry| %>
  • > <%= entry.body %>
  • <% end %> And stuff like this in your controller: def remove_entry entry = JournalEntry.find(params[:id]) update_page do |page| page[entry.dom_id].remove end end

    Debugging RJS

      // log the beginning of the requests
      onCreate: function(request, transport) {
        new Insertion.Bottom('debug', '

    [' + new Date().toString() + '] accessing ' + request.url + '

    ') }, // log the completion of the requests onComplete: function(request, transport) { new Insertion.Bottom('debug', '

    http status: ' + transport.status + '

    ' + '<pre>' + transport.responseText.escapeHTML() + '</pre>') } }); script>
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