Set instance variable param value

Question

I am learning rails and have run into bump.

I have a view that contains the following:

<span><%= @goals.cost_per_conversion %></span>

(just as an example while @goals actually contains more then just cost_per_conversion)

Under certain circumstances the view will not have the instance variable @goals. I am trying to guard against cases when this is true.

In my controller I have the following code:

if Goal.exists?(params[:id])
   @goals = Goal.find(params[:id])
else
   @goals.cost_per_conversion = 'N/A'
end

Naturally this returns an error as .conversions is not a method.

How do I set the conversions param so that my view can still work when there is no @goals variable available.

Arup Rakshit · Accepted Answer · 2015-02-17 18:57:57Z

3

Use #try :

<span><%= @goals.try(:cost_per_conversion) %></span>

And change the controller code :

@goals = Goal.find(params[:id])

Double checking record in controller is expensive. Btw, since it's a single record, you could name it @goal instead of @goals.

edited Feb 17, 2015 at 18:57

answered Feb 17, 2015 at 18:39

Arup Rakshit

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1 Comment

captainrad Over a year ago

in this case however @goals is not a single record. but your previous answer was perfect and this applies as well! Thanks

Zakaria · Accepted Answer · 2015-02-17 18:50:44Z

1

you can use if:

<% if @goals %>
    <span><%= @goals.cost_per_conversion %></span>
<% end %>

and change the controller code to:

if Goal.exists?(params[:id])
   @goals = Goal.find(params[:id])
end

or

if params[:id]
   @goals = Goal.find(params[:id])
end

answered Feb 17, 2015 at 18:50

Zakaria

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Comments

David Grayson · Accepted Answer · 2015-02-17 18:56:18Z

0

You might consider creating a new Goal object with @goals = Goal.new in case the goal could not be found in the database. Or you could make a null object that acts like a goal, following the null object pattern.

These are just two ways to approach it, and are not necessarily better than the other answers.

By the way, since your instance variable just contains one goal and not a collection of goals, it should be named @goal.

answered Feb 17, 2015 at 18:56

David Grayson

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