Creating dynamic variable in Ruby on rails

Question

I'm trying to generate a variable name based on day of week. In my html.erb file, I have the following code:

<%= "@selected_venue.open_time_"+Time.now.strftime('%a').downcase %>

I'm trying to create a variable such as "@selected_venue.open_time_mon", "@selected_venue.open_time_tue", "@selected_venue.open_time_wed", etc. As you can see, I'm appending the day of week to the generic variable name "@selected_venue.open_time_" so I can get the value of the dynamically generated variable.

Instead of getting the value that the variable represents (which is a time such as 2:00PM), I keep getting the literal result: "@selected_venue.open_time_wed".

Is there a method that I can use to get the value of the dynamically generated variable?

Mori · Accepted Answer · 2013-12-05 23:01:09Z

3

Cleaner to move the logic to a helper, e.g.:

# in a helper
def open_time
  var = "open_time_" + Time.now.strftime('%a').downcase
  @selected_venue.send(var)
end

# in the template
<%= open_time %>

I agree with @Bubbles that it's better to have a collection like a hash or an array in open_time than having to metaprogram like this.

edited Dec 5, 2013 at 23:01

answered Dec 5, 2013 at 2:39

Mori

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3 Comments

Vee Over a year ago

Mori - I ended up putting the open_time method into a helper and it worked great; however, I'm now calling the show action in my controller via AJAX and the application no longer recognizes the open_time method. Do you have any suggestions on how to access helper methods via AJAX?

Mori Over a year ago

@Vee, the helper method should have the same scope whether called by AJAX or not. If the AJAX uses a different controller you need to make sure that the helper is visible there as well, e.g. with the helper directive.

Vee Over a year ago

You're right, Mori! After modifying a good amount of code, I forgot to rename the instance variable in the helper. Again, works like a charm. Thanks!

Bubbles · Accepted Answer · 2013-12-05 02:50:48Z

2

This is more a general ruby thing, but sure it's possible. You can access a variable like so:

@selected_venue.send(:"open_time_#{Time.now.strftime('%a').downcase}")

That said, in a situation like this I'd first consider if I could replace the dynamic variable with a hash - if open_time could be a hash and if you could set :wed on it, I'd personally find it tidier (of course, I don't know the full situation here - if you have seven variables in the venue table for daily opening times, this solution would make sense).

edited Dec 5, 2013 at 2:50

answered Dec 5, 2013 at 2:07

Bubbles

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2 Comments

Vee Over a year ago

Thanks, Bubbles. Your answer worked great but I went with Mori's answer below as it allowed me to insert some additional code in the helper. Cheers!

Bubbles Over a year ago

Fair enough; there's a lot to be said for extracting the code.

Ajedi32 · Accepted Answer · 2013-12-05 14:57:27Z

0

Note that if @selected_venue is an ActiveRecord object (and open_time_mon is an attribute of that object), you can just use it like a hash:

@selected_venue["open_time_#{Time.now.strftime('%a').downcase}"]

Otherwise, as others have said you'll need to use send:

@selected_venue.send("open_time_#{Time.now.strftime('%a').downcase}")

answered Dec 5, 2013 at 14:57

Ajedi32

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