Rails ERB遍历数组

Question

I'm trying to experiment with blocks and how to iterate over collections in ERB. I have a models in a one-to-many relatinship (Channel and their corresponding types).

controller

class HomePageController < ActionController
   def index
    @channels =  Channel.all
   end
end

Then in the view, I iterate over all the attributes belonging to a Channel. When I want to print all types, this code gives me the desired output:

view

<% @channels.each do |channel| %>
    <% @types.each do |type| %>
        <%= Type.find(type).name %>
    <% end %>
<% end %>

At first I tried to achieve this by using the yield keyword in a neat one-liner but I couldn't manage to print anything to the browser, only to the console

<% @types.each {|type| yield Type.find(type).name } %>

Is there an equivalent one-liner?

Answer 1

First of all this method is so inefficient, you are doing n-queries, to find each record of type Type instead convert those into an array of types by using a single query in the controller, assume that that array is in type_ids

# controller
@channels = Channel.includes(:types) # avoiding n+1 queries

# view
<% @channels.each do |channel| %>
  # some channel info output
  <% channel.types.each do |type| %>
    <%= type.name %>
  <% end %> # types loop
<% end %> # channel loop

As @Almaron mentioned, you could render a partial for more simplification, if you have a partial called _type.html.erb you can call render directly

# view
<%= render channel.types %>

Rails will do all the iterating and rendering.

Answer 2

First of all, this kind of code does not belong to the view. Don't tackle the database from the view (in your case Type.find() ). Move it to the controller where it belongs.

The second thing to note is the difference between <%= and <% tags. The first one outputs the returned result, while the second one doesn't. The problem with .each is that it returns the object it has been used on, so in your case if you just go <%= @types.each {|type| Type.find(type).name } %> <%= @types.each {|type| Type.find(type).name } %> you'll get the @types array printed out.

If you want to simplify that code, you can use a helper method for iterating and a partial for rendering each item. That way you get something like this <% collection_iterate @items, 'item_partial' %>