Strings passed from controller to view in Rails arrive empty - ruby-on-rails

I am trying to pass a string to my view from controller like this:
controller:
def index
#str = 'foo'
end
view:
String: <% #str %>
The variable itself seems to arrive because I get no error. However, it arrives empty (only "String" is in html, nothing else). And it seems to work great with other built-in types, e.g. Time. What am I missing here? I use Ruby 2.2.1 and Rails 4.

As others have said, you need to use
<%= #str %>
I'll give you an explanation as well - you use <% %> for when you need to run some Ruby code that you don't want displayed to the screen. For example, you might have conditional logic like
<% if user_signed_in? %>
<%= #welcome_string %>
<% end %>
Use <%= %> when you want to output, drop the '=' for conditional logic or anything that doesn't need to display.

in your view
String: <%= #str %>

In view user following code:
String: <%= #str %>

In your view, use:
<%= #str %>

As the other users have pointed out, you need to use <%=
The = is an ERB flag to so export the result of the code inside of the tags and put it into the DOM.
If you want to put some logic into your page that you don't want to evaluate, you leave the = out.
<% if user_wants_to_see_output? %>
<%= "User will see this" %>
<% end %>

Related

How to return ActiveRecord Association Proxy on ERB

so I have a standard has_many through association in my models, very similar to the question here: Loop through ActiveRecord::Associations::CollectionProxy with each
I used the advice in that problem but I think I am having some trouble getting it through on my ERB file so that it shows up in my app. At the moment I have the following:
<%= #memberships.map do |a| %>
<%=a.name%>
<% end %>
In this scenario, the membership model is the one through which users and organizations have many though (#memberships = #user.organizations). So the #memberships.class returns
ActiveRecord::Associations::CollectionProxy::ActiveRecord_Associations_CollectionProxy_Organization
on the rails console. So the moment, in the browser the code returns on a page where the user is in two orgs:
orgone orgtwo["\n", "\n"]
I just don't know how to manipulate the proxy classes to return what I want. Thanks!
UPDATE:
I figured it out, I had to remove the = at the top of the block, and I added some styling with a comma:
<% #memberships.map do |a| %>
<h3><%=a.name %> <%= ", " unless a == #memberships.last %></h3>
<% end %>
If you want to print the name of each membership, what you want is
<% #memberships.each do |membership| %>
<%= membership.name %>
<% end -%>
The <% prefix in ERB executes code without appending the results to the output buffer, while the <%= prefix outputs the string representation of the result of the expression. Since each returns an enumerator, a <%= will return the string representation of the enumerator which is something like #<Enumerator:0xDEADBEEF.

In a rails view, how can I send output to view besides <%= %>?

Short version:
It seems weird to me to have rails code like, say,
<% if #list.empty
%><%= val %><%
end %>
Is there some way to do something like this?
<% if #list.empty
some_display_function_i_wish_existed val
end %>
Long version:
I have a model, tweet.rb, that overrides to_s. The to_s works fine.
I have a view that needs to output to_s for each tweet in #meme.tweets .
I've observed the following:
<% #meme.tweets.each do |tweet|
tweet
end %>
Result: no output
<% #meme.tweets.each do |tweet|
puts tweet # or tweet.to_s does the same thing
end %>
...Result: no output
<%= #meme.tweets.each do |tweet|
tweet
end %>
...Result: output is entire inspection of each tweet, not to_s
<%= #meme.tweets.each do |tweet|
puts tweet # or tweet.to_s does the same thing
end %>
...Result: output is entire inspection of each tweet, not to_s
<% #meme.tweets.each do |tweet| %>
<%= tweet %>
<% end %>
...Result: works as intended (outputs result of to_s for each tweet). So does:
<%= #meme.tweets.collect do |tweet|
tweet.to_s
end %>
...Result: works as intended.
I come from a PHP background, and don't really understand the rules here.
I know I can do it the way I did in the last example.
But could someone explain why none of the other examples work as I intend?
It seems to me that the rules APPEAR to be:
1) <%= something %> will take that thing, call to_s on it, which will default to inspect if not overridden.
2) <% something %> will execute something
Is there a way to use 2) <% %> to send output to the view?
Or is it against the rules to have <% %> tags that span multiple lines of ruby code at all?
<%= code %> will print to the the output the result of the inner code. <% %> won't print anything, it just evaluates the inner code.
That's why the first example doesn't work. On the second example you expect the puts to print the tweets, but puts doesn't print on the same buffer... (you'll see the tweets printed on the rails console instead).
On 3rd and 4th example you are printing the collection as an object (#meme.tweets.each returns an Enumerable and ERb call #to_s on that) and not the code inside the block.
The 5th form is correct. That's what you'll normally do.
The 6th form is in some way correct too. There you are iterating a collection, calling #to_s on each element and then collecting them on a new array, that gets printed to the output (but you are printing an array of strings, not just one big string).
you can get a similar result with #join. (It returns a string created by converting each element of the array to a string)
<%= #meme.tweets.join %>
<% %> are used when you do not want the Ruby code you're executing to output anything. The <%= %> tags are used when you want to output something. This is why your example using <%= %> and tweet.to_s works as intended.
If you don't specify which attribute you want to output, then yes, puts will display the whole object. If for example, you had a message attribute on your tweet object, writing tweet.message (inside of a <%= %>, of course) would output just the message attribute of that tweet.
The direct answer is the concat function, eg:
Hi, my name is <% concat("Shelvacu") %>.
which is the same as
Hi, my name is <%= "Shelvacu" %>.
Which both output Hi, my name is Shelvacu.
Think of it like this: An erb template is parsed, transformed into valid ruby code, and then that ruby code is run*. Everything that is not inside <% ... %> is converted to concat("..."), <% statement %> is converted to statement, and <%= statement %> is converted to concat(statement.to_s).
So when ERB sees
1 + 2 = <%= 1 + 2 %>
<% puts "hello" %>
<% #meme.tweets.each do |tweet| %>
<%= tweet %>
<% end %>
that code is then translated to*
concat("1 + 2 = ")
concat((1 + 2).to_s)
concat("\n\n")
puts "hello"
concat("\n\n")
#meme.tweets.each do |tweet|
concat(tweet.to_s)
end
* This is an oversimplification, ERB does much more so that errors point the right line, statements don't merge with eachother in unexpected ways, and I didn't even mention <%- ... %>. However, this should be a decent mental model for understanding whats happening when you write code in ERB.

How to obtain the same result as <%= var %> without the =?

In the Rails views, I regularly find lines like:
<%= my_var %>
What if I had a slightly more complex situation and I needed to trigger the printing with plain code instead of <%= %>?
Example:
<% .....
puts my_var
%>
I guess is a silly question but bear with me, I'm a ruby beginner.
Look at documentation of ERB
In <% %> you put expressions that are not for printing out.
In <%= %> you put code for printing out.
Example:
<% if #cost < 10 %>
<b>Only <%= #cost %>!!!</b>
<% else %>
Call for a price, today!
<% end %>
You can use helper method which is much more cleaner.

Rails 'params' variable

In reference to this
I've created a question in a webform like this:
<div class="form_row">
<label for="features[]">Features:</label>
<% [ 'scenarios', 'role_profiles', 'private_messages', 'polls' ].each do |feature| %>
<br><%= check_box_tag 'features[]', feature,
(params[:features] || {}).include?(feature) %>
<% end %>
</div>
So if scenarios and private_messages gets checked and I print out params[:features] I will get:
scenariosprivate_messages
I was wondering how would I be able to obtain scenarios and private_messages separately from params. Is the mapping params[:features] = "scenariosprivate_messages" or is it really params[features] = ["scenarios", "private_messages"] ? If it's the latter how can I loop through them?
I write in my view:
<%= params[:features].each {|param|
param.capitalize
} %>
and I still just get scenariosprivate_messages printed.
Try this instead:
<% params[:features].each do |param| %>
<%= param.capitalize %>
<% end %>
The problem with your original solution is that you're printing out the result of the block, which is the array itself, rather than printing out each element of the array.
You shouldn't be using params in your views. You're best off assigning params[:features] to an instance variable in your controller and then iterating over that in your view.
But to answer your question, you're putting the equals sign for output in the wrong place. You want to output each element of the array individually instead of outputting the result of the loop.
You must use humanize:
<% params[:features].each do |param| %>
<%= param.humanize %>
<% end %>
According to this blog post you should be able to access them individually as params[:features]['scenarios'] etc. Looping should just work like with all other arrays -- eg
params[:features].each { |param|
# do something with param
}

Rails check if yield :area is defined in content_for

I want to do a conditional rendering at the layout level based on the actual template has defined content_for(:an__area), any idea how to get this done?
#content_for_whatever is deprecated.
Use content_for? instead, like this:
<% if content_for?(:whatever) %>
<div><%= yield(:whatever) %></div>
<% end %>
not really necessary to create a helper method:
<% if #content_for_sidebar %>
<div id="sidebar">
<%= yield :sidebar %>
</div>
<% end %>
then of course in your view:
<% content_for :sidebar do %>
...
<% end %>
I use this all the time to conditionally go between a one column and two column layout
<%if content_for?(:content)%>
<%= yield(:content) %>
<%end%>
Can create a helper:
def content_defined?(var)
content_var_name="#content_for_#{var}"
!instance_variable_get(content_var_name).nil?
end
And use this in your layout:
<% if content_defined?(:an__area) %>
<h1>An area is defined: <%= yield :an__area %></h1>
<% end %>
Ok I am going to shamelessly do a self reply as no one has answered and I have already found the answer :)
Define this as a helper method either in application_helper.rb or anywhere you found convenient.
def content_defined?(symbol)
content_var_name="#content_for_" +
if symbol.kind_of? Symbol
symbol.to_s
elsif symbol.kind_of? String
symbol
else
raise "Parameter symbol must be string or symbol"
end
!instance_variable_get(content_var_name).nil?
end
I'm not sure of the performance implications of calling yield twice, but this will do regardless of the internal implementation of yield (#content_for_xyz is deprecated) and without any extra code or helper methods:
<% if yield :sidebar %>
<div id="sidebar">
<%= yield :sidebar %>
</div>
<% end %>
I use #view_flow and value of the content method before checking if the content is present in the view like this:
#view_flow.content[:header_left_or_whatever_the_name_of_your_block_is].present?
Recently stumbled upon it when showing all local, global and instance variables of self in the console with byebug. I’m a fan using this because it’s straight from Rails, won’t throw an error, won’t hide anything w “Rails magic”, returns a definite true or false, + only checks the content in the current context of the view being rendered.
#view_flow is an instance attribute of ActionView::Context and because Action View contexts are supplied to Action Controller to render a template it will be available to any view that has been rendered by Rails. Although it checks for content, the content_for block will not be yielded if it isn’t there. So it’s been my perfect solution in similar situations.

Resources