Conditionally add a class to link_to in Rails - ruby-on-rails

Question

I want to conditionally add the class "hidden" to a Rails link tag, depending on if "accepted == true".
If I weren't using a rails link_to I could do <a href="#" class="foo bar <%= "hidden" if accepted == true %>" >. How can I accomplish this inside a link_to?
<%= link_to "Accept Friend Request",
"#",
class: "btn btn-success btn-sm btn-block requestSent ???hidden???",
disabled: true %>

Answer 1

If you use interpolation with #{}, anything you put between it is run as plain old Ruby code.
In this example you could add a conditional class in the string like this:
<%= link_to "Accept Friend Request",
"#",
class: "btn btn-success btn-sm btn-block requestSent #{'hidden' if accepted}",
disabled: true %>
Just note that you should use single quotes around the class name 'hidden'.
Also note that when a variable represents a boolean value (true or false), you don't need to explicitly say if accepted == true. You can simply say if accepted.

Answer 2

You can do it outside the link_to:
<% css_class = accepted ? "hidden" : "" %>
<%= link_to "Accept Friend Request",
"#",
class: "btn btn-success btn-sm btn-block requestSent #{css_class}",
disabled: true %>

Answer 3

You can use a helper to build up the link as well:
def accept_friend_request_link
classes = [:btn, :and_friends]
if accepted
classes << :hidden
end
link_to 'Accept Friend Request', '#', class: classes, disabled: true
end

Answer 4

I posted a similar answer to this question.
A cleaner solution
The standard approach requires putting logic into the views and using string interpolation or moving things into a separate helper.
Here's an updated approach that avoids any of that:
<%= link_to "Accept Friend Request",
"#",
class: class_string("btn btn-success btn-sm ban-block requestSent" => true, hidden: accepted),
disabled: true %>
class_string method
The class_string helper takes a hash with key/value pairs consisting of CSS class name strings and boolean values. The result of the method is a string of classes where the boolean value evaluated to true.
Sample Usage
class_names("foo bar" => true, baz: false, buzz: some_truthy_variable)
# => "foo bar baz"
Inspired by React
This technique is inspired by an add-on called classNames (formerly known as classSet) from Facebook’s React front-end framework.
Using in your Rails projects
As of now, the class_names function does not exist in Rails, but this article shows you how to add or implement it into your projects.

Answer 5

I've override the link_to to expect a class_if parameter, check it out:
def link_to(options = {}, html_options = {})
if html_options.is_a?(Hash) && html_options.key?(:class_if)
html_options[:class] <<
(" #{html_options[:class_if][1].strip}") if html_options[:class_if][0]
html_options.delete :class_if
end
super(options, html_options)
end
And usage:
<%= link_to(my_path, class: "class1", class_if: [true_or_false?, 'class2']) %>
I've just override one method, but a good refactor is to override all of described signatures here: http://api.rubyonrails.org/classes/ActionView/Helpers/UrlHelper.html#method-i-link_to
UPDATE
Another solution is:
module ApplicationHelper
def active_link_to(name = nil, options = nil, html_options = nil, &block)
html_options ||= { class: '' }
html_options[:class].concat('is-active') if options.match(controller_name)
link_to(name, options, html_options, &block)
end
end
And usage:
<%= active_link_to(my_path, 'My path') %>
This way, I got an "active status" even when is a custom route like: "my_path/help", "my_path/two".