Good notes posted by hosiawak

Naming fragment cache

One of the common ways of using fragment caching is to cache content that’s shared across the site (eg. left navigation, menus, widgets etc.) that looks and works the same regardless of the name of the action or controller calling it. In such cases it’s very easy to just use named fragment caching eg.:

<% cache('left_nav') do -%>
  <%= display_left_nav -%>
<% end -%>

stub_chain is very useful when testing controller code

or any other chained method call type that you’d like to stub, example:

in your controller:

def new
  @user = current_site.users.new
end

in your spec:

it "#new should assign a @user" do 
  u = mock("User")
  controller.stub_chain(:current_site, :users, :new).and_return(u)
  assigns[:user].should == u
end

whereas before you had to stub each chained method call separately:

it "#new should assign a @user" do 
  u = mock("User")
  users = mock("Users collection", :new => u)
  site = mock("Site", :users => users)
  controller.stub!(:current_site).and_return(site)
  assigns[:user].should == u
end

Please note that stub_chain was added to RSpec in version 1.2.6

A catch-all format

If you’d like to specify a respond_to only for 1 or a few formats and render something else for all other formats, eg: (action.rss returns a feed but action.html or action.js should just render 404), use format.all:

respond_to do |format|
  format.rss { render_rss }
  format.all { render_404 }
end

Rails will render an empty string for all formats that don’t specify a response explicitly.

Universal partial

polymorphic_url is very useful if you want to create an universal partial that works for more than 1 type of object passed to it.

For example in you sidebar you might have a _sidebar.html.erb partial that’s supposed to display links to “Edit” and “Delete” actions. You can write it in such a way that it can be reused for different types of objects (in the example below we pass either a Post or a Note).

your_template.html.erb

<%= render :partial => 'shared/sidebar', :locals => { :obj => Post.new -%>

other_template.html.erb

<%= render :partial => 'shared/sidebar', :locals => { :obj => Note.new -%>

_sidebar.html.erb

<%= link_to "Edit", polymorhpic_url(obj, :action => 'edit') -%>
<%= link_to "Delete", polymorphic_url(obj), :method => :delete -%>

Useful in migrations

The most common usage pattern for this method is probably in a migration, when just after creating a table you want to populate it with some default values, eg:

class CreateJobLevels < ActiveRecord::Migration
  def self.up
    create_table :job_levels do |t|
      t.integer :id
      t.string :name

      t.timestamps
    end

    JobLevel.reset_column_information
    %w{assistant executive manager director}.each do |type|
      JobLevel.create(:name => type)
    end
  end

  def self.down
    drop_table :job_levels
  end
end

Helper method taking a block

Following the similar egzample by autonomous, here’s a simpler version when you just need to write a flexible helper method that takes a block.

For example, suppose you have a method that renders a tree:

def render_tree(ary, &block)
  concat("<ul>", block.binding)
  for elem in ary
    concat("<li>", block.binding)
    yield elem
    concat("</li>", block.binding)
  end
  concat("</ul>", block.binding)
end

You can use it in your view, eg:

<% render_tree(@objects) do |elem| -%>
  <%= elem.title -%>
  <%= link_to 'delete', elem -%>
<% end -%>

that would return for egzample:

<ul>
  <li>
    Test title
    <a href="delete">/elems/1</a>
  </li>
</ul>

Testing concat

To test such helper methods, use the following pattern (a utility method added to your Rspec/unit test suite:

def render_for(root, options = {})
  _erbout = ''
  render_tree(root, options) do |node|
    _erbout.concat(node.title)
  end
  _erbout
end

and test like this (RSpec example):

it "should return abc" do
  render_for(object).should == 'abc'
end

Overriding the default div class="fieldWithErrors"

By default fields that are invalid are wrapped in:

<div class="fieldWithErrors">
  <input type="text" name="blah">
</div>

To override and wrap in spans instead of divs place the following in your environment.rb:

ActionView::Base.field_error_proc = Proc.new { |html_tag, instance| "<span class=\"fieldWithErrors\">#{html_tag}</span>" }

or to not use wrapping at all:

ActionView::Base.field_error_proc = Proc.new { |html_tag, instance| "#{html_tag}" }

Overriding the default div class="fieldWithErrors"

By default fields that are invalid are wrapped in:

<div class="fieldWithErrors">
  <input type="text" name="blah">
</div>

To override and wrap in spans instead of divs place the following in your environment.rb:

ActionView::Base.field_error_proc = Proc.new { |html_tag, instance| "<span class=\"fieldWithErrors\">#{html_tag}</span>" }

or to not use wrapping at all:

ActionView::Base.field_error_proc = Proc.new { |html_tag, instance| "#{html_tag}" }