Is there an inline way to conditionally add an attribute in Ruby? - html

Question

There are a number of times in Rails when I would like to be able to add an attribute to something only if the attribute is of a particular value.
Let me give you an example. Let's say I want to disable a button based on a particular property such as check_if_user_can_be_added:
link_to 'Create account', new_user_path, disabled: (user_can_be_added?)
This all looks fine and well except that disabled happens to be applied in HTML regardless of what value you give it. If you give a button the attribute disabled: false then it will still be disabled.
What I need
# if the button is disabled
link_to 'Create account', new_user_path, disabled: true
# if the button is not disabled
link_to 'Create account', new_user_path
The way that I can see to do it
Getting this means that you need a solution similar to the following which sets up the options hash first and then passes it in subsequently:
options = user_can_be_added? ? {disabled: true} : {}
link_to 'Create account', new_user_path, options
The way I would like to do it...
This doesn't work but trusting in Ruby's beauty I suspect there's something similar out there. This is basically what I'd like to do
link_to 'Create account', new_user_path, ({disabled: true} if user_can_be_added?)
Can I do it, is there perhaps something using the splat operator that gets me there...?

Answer 1

You can just set nil to cause Rails to ignore the attribute:
link_to 'Create account', new_user_path, disabled: (user_can_be_added? ? true : nil)
For this particular case, you can also use || like so:
link_to 'Create account', new_user_path, disabled: (user_can_be_added? || nil)

Answer 2

I'm not familiar with rails, but inline if statements can be achieved as follows in ruby:
(condition ? true : false)
I would assume your code would look like this:
link_to 'Create account', new_user_path, (user_can_be_added? ? disabled: true : nil)
This would essentially pass in nil in place of disable: true if user_can_be_added? resolves to false.
I'm not sure how the link_to function would handle that, though. I guess the reason disabled: false doesn't work, is the link_to function recieves a hash of attributes as the final parameter, which are applied to an html link. Since the disabled attribute in html doesn't need a value, it would just stick in <a href="" disabled> regardless of its value. Someone feel free to correct me though, I haven't used rails.

Answer 3

Years ago I used a Rails plugin for HTML attributes that is still available on Github. That plugin allowed to write html tags like this:
content_tag(:div, :class => { :first => true, :second => false, :third => true }) { ... }
# => <div class="first third">...
Plugins are unsupported by current versions of Rails and plugin only worked for tag helpers, but perhaps this helps you to write a helper yourself.

Answer 4

For many arguments, using the splat will work:
p "Here's 42 or nothing:", *(42 if rand > 0.42)
This won't work for a hash argument though, because it will convert it to an array.
I wouldn't recommend it, but you could use to_h (Ruby 2.0+):
link_to 'Create account', new_user_path, ({disabled: true} if user_can_be_added?).to_h

Answer 5

To me that looks like a great place to use a helper
module AccountHelper
def link_to_create_account disabled = false
if disabled
link_to 'Create account', new_user_path, disabled: true
else
link_to 'Create account', new_user_path
end
end
end
In your ERB it's simply link_to_create_account(user_can_be_added?)
Not everyone likes helpers, but they work for me.