Ruby-on-rails – ActiveAdmin — How to access instance variables from partials

activeadminruby-on-railsruby-on-rails-3ruby-on-rails-3.1

I can't seem to access instance objects in partials. Example:

In controller I have:

ActiveAdmin.register Store do
  sidebar "Aliases", :only => :edit do
    @aliases = Alias.where("store_id = ?", params[:id])
    render :partial => "store_aliases"
  end
end

Then in the _store_aliases.html.erb partial I have:

<% @aliases.each do |alias| %>
  <li><%= alias.name %></li>
<% end %>

This doesn't work. The only thing that does work (which is horrible to do as I'm putting logic in a view is this:

  <% @aliases = Alias.where("store_id = ?", params[:id]) %> 
  <% @aliases.each do |alias| %>
     <li><%= alias.name %></li>
  <% end %>

Best Answer

When rendering a partial you need to actively define the variables that are given to that partial. Change your line

render :partial => "store_aliases"

render :partial => "store_aliases", :locals => {:aliases => @aliases }

Inside your partial the variables is then accessible as a local variable (not an instance variable!). You need to adjust your logic inside the partial by removing the @.

<% aliases.each do |alias| %>
  <li><%= alias.name %></li>
<% end %>

For further reading have a look at the API documentation (specifically the section "3.3.4 Passing Local Variables").

Related Solutions

Ruby-on-rails – Rails: Should partials be aware of instance variables

In recent versions of Rails it is quite a bit easier to render partials and pass locals to them. Instead of this.

<%= render :partial => 'form', :locals => { :item => @item } %>

You can do this.

<%= render 'form', :item => @item %>

I don't do this in the Nifty Scaffold generator to keep backwards compatibility, but I'll change this in a future release.

As for whether it's acceptable to use instance variables in partials. I think it is. In all practicality, what is the downside? Certainly things can get out of hand if you aren't consistent, but I like to apply these guidelines.

Never create an instance variable just to share it between partials. Usually this means you will only be sharing the controller resource object.
If the partial is the same name as the resource, pass it as a local with <%= render @item %>.
If the partial will be shared across multiple controllers then only use locals.

This is what works well for me anyway.

Bonus tip: if you find yourself passing in a lot of locals into a partial and you want some of them to be optional, create a helper method which renders the partial. Then always go through the helper method so you can make a clean interface with optional args for rendering the partial.

Jquery – Rendering Rails Partial from AJAX and passing in local variables from AJAX

Client

According to the $.get and $.ajax docs, params will go into the query string part of the URL:

// request to /somethings?a=abc&b=2
$.get('/somethings', {a: 'abc', b: 2})

Server

Query string parameters can be accessed from Rails actions via a Hash-like object called params. [1]

class SomethingsController < ApplicationController
  def index
    puts params[:a] # if URL was /somethings?a=123, will print 123
  end
end

Putting it Together

Let's make a complete example with a partial.

Here is the client code:

// client call to /somethings?name=Something+123
$.get('/somethings', {name: 'Something 123'}, function(data){
  $('#target').html(data);
});

Here is the server:

class SomethingsController < ApplicationController
  def index
    # bind controller variable @name
    @name = params[:name]
  end
end

Inside the view app/views/somethings/index.html.erb:

<%= render :partial => 'some_partial', :locals => {:name => @name} %>

I've moved the partial rendering into a view. I think rendering partials from views is more standard than rendering partials directly from controllers.

Best Answer

Related Solutions

Ruby-on-rails – Rails: Should partials be aware of instance variables

Jquery – Rendering Rails Partial from AJAX and passing in local variables from AJAX

Related Topic