esoppus I suppose

Inserting a rake dependency first

Usually, if you’re trying to extend a rake task by adding new dependencies to it you just redefine the task with the new dependency.

namespace :tickle do
  task :cow => 'relax'
end

So if originally tickling the cow would first milk it, typing rake tickle:cow will now:

1. Milk the cow
2. Relax the cow
3. Tickle the cow

If you instead want the relaxing to happen first, you have to go straight at the definition of the task and alter its prerequisites. These prerequisites are just an array of task names, so to make your new task happen first, just insert your task at the beginning.

# fetch the task definition
task = Rake::Task['tickle:cow']
# insert our new prerequisite at the beginning
task.prerequisites.insert(0, 'relax')

A real-life example of this is if you want to pull some data down before resetting your database with a rake db:migrate:reset. If you define a task like rake data:retrieve and don’t want to remember to do rake data:retrieve db:migrate:reset you can insert data:retrieve as an early prerequisite for db:migrate:reset.

Rake::Task['db:migrate:reset'].prerequisites.insert(0, 'data:retrieve')

And if you have to do this a lot, this may be handy

module Rake
  module OrderedPrerequisites
    def require_first(*tasks)
      prerequisites.insert(0, *tasks)
    end
  end
 
  class Task
    include OrderedPrerequisites
  end
end

And now you can do

Rake::Task['db:migrate:reset'].require_first('data:retrieve')