Upgrading to v4

With version 4, we've removed a lot of lesser used features in the core and replaced them with better-supported approaches which already existed or moving that functionality into an extension.

Here's the list of API changes:

Lots of code was touched during the v4 refactor. If you were relying on internal methods which were not mentioned above or described on this documentation site, there is a possibility things have changed. Please reach out if you have questions.

Environments and Changes to configure blocks.

v4 adds the ability to differentiate between different target environments. In the past, we conflated the environment development and the output mode build as the two ways to target config changes.

What we are doing in v4 separates these. There are 2 default environments now, development and production, but you can easily add your own. There are 2 default output modes as well, server and build.

The middleman server command defaults to the mode of server and the environment of development.

The middleman build command defaults to the mode of build and the environment of production.

The configure command can target both environments and modes:

configure :server { #enable sprockets debugging }
configure :build { # run some post-build hooks }
configure :development { # enable some sass debug settings }
configure :production { activate :minify_html }

This adaptation will probably affect the largest number of Middleman users.

Like Rails, we support automatically loading environment specific config from a predefined path. If you have a lot of production config, create a file at environments/production.rb and its contents will automatically be evaluated when in production.

It is also possible to change the environment regardless of the output mode. So now, you can preview the production output in the dev server: middleman server -e production

The -e environment flag is also used for custom environments. Say you want to push some code to staging, you could use: middleman build -e staging and the environments/staging.rb could have staging-specific deploy scripts.

File Updates in Rack servers

This refactor allows Middleman to run as a Rack server and still update on file changes normally. This makes mounting inside Rails or using the Pow server much nicer.

Installing Project Templates from Git


During middleman init, custom project templates from ~/.middleman or gems are no longer supported. Project templates must be git repositories.

Project template repository on GitHub:

middleman init MY_PROJECT_FOLDER -T username/repo-name

Local project template repository:

middleman init MY_PROJECT_FOLDER -T file:///path/to/local/repo/

External Tools

We want to support as many possible tools as we can. Want to run Grunt? Maybe ClojureScript JVM in the background? How about browserify or ember-cli? That's what the goal of external_pipeline is. Here's an example of how Middleman v4 can control an external process, which outputs into an arbitrary directory and is then consumed by Middleman:

activate :external_pipeline,
  name: :ember,
  command: "cd test-app/ && ember #{build? ? :build : :serve} --environment #{config[:environment]}",
  source: "test-app/dist",
  latency: 2

This feature is hosted on top of a lower-level feature which allows multiple directories to be overlaid to create the combined sitemap for Middleman. This is great for keeping things like bower_components separate from your source directory, but still available to Middleman:

import_path File.expand_path('bower_components', app.root)


The final new feature is "Collections". Collections abstract some logic from Middleman Blog to allow you to define groups of files and paths, in pure Ruby, which can then be acted upon. This works around a common new user mistake where they assume config.rb is executed whenever anything changes, rather than once on startup. Collections give the illusion that anything you write in config.rb is always up to date.

Lets say you want to implement tagging:

def get_tags(resource)
  if resource.data.tags.is_a? String

def group_lookup(resource, sum)
  results = Array(get_tags(resource)).map(&:to_s).map(&:to_sym)

  results.each do |k|
    sum[k] ||= []
    sum[k] << resource

tags = resources
  .select { |resource| resource.data.tags }
  .each_with_object({}, &method(:group_lookup))

collection :all_tags, tags
collection :first_tag, tags.keys.sort.first

This will give you an always up-to-date hash called all_tags and an always up-to-date array representing the current resources which have the first alphabetical tag. As you can see, all the code is normal Ruby, so you can write your implementation however you'd like. The only 2 constraints are that a collection must be made from a chained collection starting with resources and that the collection method must be called when you are done to pass the information into your templates.

<% collection(:tags).each do |k, items| %>
  Tag: <%= k %> (<%= items.length %>)
  <% items.each do |article| %>
    Article: <%= article.data.title %>
  <% end %>
<% end %>

First Tag: <%= collection(:first_tag) %>

Collections can also be used, directly in config.rb to keep dynamic pages up-to-date:

tags.each do |k, articles|
  proxy "/tags/#{k}.html", "/tags/list.html", locals: {
    articles: articles

Again, Collections are very new and experimental. You can help influence the direction of the feature over the beta period.

Extension API Improvements

Context Methods

In v4, the Application, Template Context and Config Context are all separated to avoid polluting a single shared instance with different concerns. In the past, it was possible for templates to add instance variables to the App, which resulted in some nasty naming collisions.

Now, each context has it's own sandbox. Extensions may want to add methods to these scopes:

Simple Resource Creation

manipulate_resource_list is great, but often more complex than most extensions need. Now, we have a way to simply create a resource with string contents.