How do I dynamically assign a variable in Ruby on Rails?

Question

I would like to highlight a table header depending on a variable's name passed in via the params.

In the controller I have:

case sort
    when 'grade'
        @sort_by_grade = 'highlight'
    when 'student_name'
        @sort_by_student_name = 'highlight'
end

Is there a more elegant way to do this? For instance, something like:

"sort_by_#{sort}" = 'highlight'

My table headers code are something like this in Haml:

%th{:class => @sort_by_grade}

What code are you using in the view? Do you have a CSS class called "highlight"? — GMA
– GMA, Commented Oct 29, 2013 at 3:16
And is the sort variable coming from something like params[:sort]? — GMA
– GMA, Commented Oct 29, 2013 at 3:16
I'd say a more elegant approach would be to use a view helper. Could you output the code for your table headers? — user419017
– user419017, Commented Oct 29, 2013 at 3:16
Yes, I do have a css class for highlight. The above code works, since in the view the th tag will have the class like the variable name. I just wish I could use meta programming to dynamically select which @sort_by variable I should use — gaudi_br
– gaudi_br, Commented Oct 29, 2013 at 3:26
Show us the code for the table headers. The highlight should be managed entirely from within the view and helpers. Not the controller. — user419017
– user419017, Commented Oct 29, 2013 at 3:30

Phrogz · Accepted Answer · 2013-10-29 03:43:46Z

2

Direct answer to your question (not best practice):

instance_variable_set :"@sort_by_#{sort}", 'highlight'

But really, using a hash or other better data structure is a better answer.

answered Oct 29, 2013 at 3:43

Phrogz

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2 Comments

gaudi_br Over a year ago

guess that's the answer I was originally looking for, but I do agree that the next answer is better... thanks Damien

user419017 Over a year ago

@gaudi_br to be fair, I've covered both in my answer, and I already answered in the comments. Anyway, I sincerely suggest you avoid using the above technique and use a view helper. That's what they're for.

score 1 · Accepted Answer · 2013-10-29 03:47:08Z

1

As I detailed in the comments, which is hacky and bad practice:

instance_variable_set("@sort_by_#{sort}", "highlight")

Personally, I wouldn't manage the highlight logic from within the controller. Extract it into a view helper or put the logic directly in the view:

%th{class: ('highlight' if params[:sort] == 'grade')}

Or, using a view helper:

application_helper

def sort_highlight(col)
  "highlight" if params[:sort] == col
end

view

%th{class: sort_highlight('grade')}

edited Oct 29, 2013 at 3:47

answered Oct 29, 2013 at 3:42

user419017

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