updates-for should respect url and only params on each element

[leastbad]

This PR used to be #182.

Reworked updates-for element to allow per-block url and only attributes. URL fragment indexes are now tracked on a per-URL basis.

That means the following contrived example works as you'd expect:

index.html.erb

<%= updates_for current_user, :posts do %>
  <% Post.all.each do |p| %>
    <p><%= p.name %>, <%= p.email %></p>
  <% end %>
  <p><%= rand(1..1000) %></p>
<% end %>

<%= updates_for current_user, :posts, only: [:name] do %>
  <% Post.all.each do |p| %>
    <p><%= p.name %>, <%= p.email %></p>
  <% end %>
  <p><%= rand(1..1000) %></p>
<% end %>

<%= updates_for current_user, :posts, url: "/updates_for" do %>
  <% Post.all.each do |p| %>
    <p><%= p.name %>, <%= p.email %></p>
  <% end %>
  <p><%= rand(1..1000) %></p>
<% end %>

<%= updates_for current_user, :posts, only: [:name], url: "/updates_for" do %>
  <% Post.all.each do |p| %>
    <p><%= p.name %>, <%= p.email %></p>
  <% end %>
  <p><%= rand(1..1000) %></p>
<% end %>

updates_for.html.erb

<%= updates_for current_user, :posts do %>
  <p>HAIRY!</p>
  <p><%= rand(1..1000) %></p>
<% end %>

No, I don't know why Post has a name and email. Don't ask hard questions.

post = current_user.posts.create name: "Fred", email: "fred@gmail.com"
post.update name: "Frederick" # updates the first three blocks, plus console warning
post.update email: "frederick@gmail.com" # updates only the first and third

Note that the 4th block will not be updated because updates_for.html.erb only has one block; a warning is generated in the console to suggest that there wasn't enough elements for the update to complete.

Unfortunately this will certainly clash with #181 as written, although I have done my best to maintain the general structure and naming to ease merge conflicts.

[marcoroth]

This PR is now published as a dev-build. To use it to your project, run:

yarn add cable_ready@https://github.com/cableready/dev-builds/archive/cable_ready/07da548.tar.gz