Exit rails gracefully if conditions are met? - ruby-on-rails

Question

I have a code where I would need to exit (php version of die), if certain events occur
Snippet in trace_controller.rb
def show
rule=Rule.new
#order,#order_error=rule.get_order(#order_external_id)
#order_items, #order_items_error=rule.get_order_items(#order)
#order_item_units, #order_item_units_error=rule.get_order_item_units(#order_items)
#outbound_messages, #outbound_messages_error = rule.check_outbound_messages(#order_external_id)
#inbound_messages, #inbound_messages_error = rule.check_inbound_messages(#outbound_message)
......
In show.html.erb
<% unless #order_error.blank? %>
<%= #order_error.html_safe %>
<% else %>
<%= render "trace/display_tabular_data", :data => #order %>
<% end %>
.....
.....
<% unless #order_items_error.blank? %>
<%= #order_items_error.html_safe %>
<% else %>
<% #order_items.each do |order_item| %>
<h5>Order Item</h5>
<%= render "trace/display_tabular_data", :data => order_item %>
<% end %>
<% end %>
......
Most of my functions are dependent on outcome of previous functions. Now take get_order_items function which is dependent on orders. If the order does not exist, there is no need to calculate get_order function as it won't exist either. Additionally, it fires up an error, as it says I am passing it a NIL object when I perform operations on orders inside get_order_item.
Additionally in the show.html.erb - #order_items, and #order_items_error should not even exist if the order does not exist. I just wanna render the function till the order_error, and then stop.
Now, coming from PHP background, I forgot that rails does not have die. So is there an alternate of die? Abort isn't it. I need it to exit disgracefully. Or is my best shot using conditionals if, unless etc...But it will look ugly as the page will become full of them. How would you about it?

Answer 1

To cut off the current action and render the view, you can use return. This will crash with errors if you try to use an unitialized instance variable in the view though.
You can also use render nothing: true which stops the current action and renders nothing.
Perhaps consider redirecting back as well:
flash[:error] = 'There was no order!'
redirect_to :back

Answer 2

I am not sure what exactly you want to do. But this should meet with what you are asking for.
def show
rule=Rule.new
#order,#order_error=rule.get_order(#order_external_id)
unless #order.blank?
#order_items, #order_items_error=rule.get_order_items(#order)
#order_item_units, #order_item_units_error=rule.get_order_item_units(#order_items) unless #order_items.blank?
end
#outbound_messages, #outbound_messages_error = rule.check_outbound_messages(#order_external_id)
#inbound_messages, #inbound_messages_error = rule.check_inbound_messages(#outbound_message) unless #outbound_messages.blank?
end
Similarly, you can add conditions in your view file:
<% unless #order.blank? %>
<% unless #order_error.blank? %>
<%= #order_error.html_safe %>
<% else %>
<%= render "trace/display_tabular_data", :data => #order %>
<% end %>
.....
.....
<% unless #order_items.blank? %>
<% unless #order_items_error.blank? %>
<%= #order_items_error.html_safe %>
<% else %>
<% #order_items.each do |order_item| %>
<h5>Order Item</h5>
<%= render "trace/display_tabular_data", :data => order_item %>
<% end %>
<% end %>
<% end %>
.......
.......
<% end %>
It is just a basic idea what I get from your example, though it was not clear enough to show what you want to achieve. So, whole idea is to check the variable before using it!
One more point I would like to mention, avoid using unless - else, unless should be used alone, if you need to put some logic in else block, why not use if - else. That probably makes more sense than unless - else.