Error messages from model in Rails 3.2 - ruby-on-rails-3

Question

Currently my app includes the following code to display the error messages on a view from model.rb but it is not updated code as error_messages_for is deprecated in Rails 3. Can anyone please suggest me how to do the same in Rails 3?? I want the logic to be in model.rb file and from there I should be able to display error msgs on view
excel_file.rb(model.rb)
#jus some sample function
def show_error(test_file)
if test_file == 'Upload Test Case'
errors[:base] << "Please upload excel sheet with testsuite config sheet and testcases"
elsif test_file == 'Upload Test Data'
errors[:base] << "Please upload excel sheet with test data"
end
end
sampleview.html.erb
#some code..
<span class='error'><%= error_messages_for (#excel_file) %></span>
#some code..
application_helper.rb
def error_messages_for(*objects)
html = ""
objects = objects.map {|o| o.is_a?(String) ? instance_variable_get("##{o}") : o}.compact
errors = objects.map {|o| o.errors.full_messages}.flatten
if errors.any?
html << "<div id='errorExplanation'><ul>\n"
errors.each do |error|
html << "<li>#{h error}</li>\n"
end
html << "</ul></div>\n"
end
html.html_safe
end

Answer 1

You could use https://github.com/rails/dynamic_form.
It provides the functionality you want.
Update
You are right, this is not in accordance to Rails 3.
You should probably do something like this:
Create a shared partial
/app/views/shared/_error_messages.html.erb
<% if target.errors.any? %>
<div id="errorExplanation">
<h2><%= pluralize(target.errors.count, "error") %> prohibited this record from being saved:</h2>
<ul>
<% target.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
And call it like this:
<%= render "shared/error_messages", :target => #excel_file %>
So why are the methods error_messages_for and f.error_messages removed? Ryan bates says the following:
The reason that the methods have been removed is that the display of the error messages often needs to be customized and doing this through the old methods was a little bit cumbersome and not as flexible as having the error message HTML inline as we have now. Having the HTML to hand in the views means that we can change the display of the error messages however we like.
source: http://asciicasts.com/episodes/211-validations-in-rails-3
Update 2
This works for custom validations the same way
validate :show_error
def show_error
if test_file == 'Upload Test Case'
errors[:base] << "Please upload excel sheet with testsuite config sheet and testcases"
elsif test_file == 'Upload Test Data'
errors[:base] << "Please upload excel sheet with test data"
end
end

Answer 2

Solution:
Create a shared partial
app/views/common/_error_messages.html.erb:
<% if target.errors.any? %>
<div id="errorExplanation">
<h2><%= pluralize(target.errors.count, "error") %> prohibited this record from being saved:</h2>
<ul>
<% target.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
And call it like this:(in sampleview.html.erb)
<% if #excel_file %>
<%= render "common/error_messages", :target => #excel_file %>
<% end %>
Put up the if condition to avoid the error NoMethodError:Undefined method 'errors' in target.errors.any?. This avoids the page from throwing this error and renders the partial view only when an instance of target(#excel_file) is present.
This works for custom validations the same way
In excel_file.rb(model.erb) in app/model:
def show_error
if test_file == 'Upload Test Case'
errors[:base] << "Please upload excel sheet with testsuite config sheet and testcases"
elsif test_file == 'Upload Test Data'
errors[:base] << "Please upload excel sheet with test data"
end
end
This worked perfectly! Now I'm able to get the error notifications properly :)