My db.rake with multi-environment db:rebuild and db:truncate. Some strange behavior in ActiveRecord `database_tasks.rb` adds to the confusion. See this StackOverflow post in the comment.

db.rake

namespace :db do
  # Rake::Task['db:load_config'].enhance [:environment]

  desc 'Truncate all tables'
  task :truncate => :environment do

    puts 'Truncating: '
    ActiveRecord::Base.connection.tables.each do |table|

      unless %w(schema_migrations rails_admin_histories).include? table
        t = table.classify
        puts "\t#{t}"
        ActiveRecord::Base.connection.execute("TRUNCATE TABLE #{table};")
        #t = t.constantize # this had problems on gem-based models i.e. tagging
        #t = t.destroy_all
      end
    end
  end

  desc 'Rebuild dev and test'
  task :rebuild, [:parallel] do |t, args|
    rebuild_env(:development, args)
    #print_tables()
    rebuild_env(:test)
    #print_tables()
  end

  desc 'Rebuild dev'
  task :rebuild_dev, [:parallel] do |t, args|
    rebuild_env(:development, args)
  end

  desc 'Rebuild test'
  task :rebuild_test, [:parallel] do |t, args|
    rebuild_env(:test, args)
  end

  desc 'Rebuild staging'
  task :rebuild_staging do
    rebuild_env(:staging)
  end

  private

  def current_db
    begin
      ActiveRecord::Base.connection.current_database
    rescue
    end
  end

  def assert_correct_db
    env = Rails.env
    db = current_db
    puts "current database[#{db}] for env[#{env}]"
    correct = false
    if Rails.env.test?
      correct = db.include? '_test'
    elsif Rails.env.development?
      correct = db.include? '_dev'
    elsif Rails.env.staging?
      correct = db.include? '_stag'
    else
      raise "Unknown db[#{db}] to match env[#{env}]"
    end

    raise "Unexpected database[#{db}] for env[#{env}]" unless correct
    #puts "Correct database[#{db}] for env[#{env}]"
  end

  def print_tables

    puts "\n\tTables in [#{current_db()}]:"
    puts "\t-----------------------------"
    connection = ActiveRecord::Base.connection
    #ap connection
    #puts "current database[#{connection.current_database}]"
    connection.tables.each do |table|
      t = table.classify
      puts "\t\t#{t}"
    end
    #puts '----------------------------------------------------------'
  end

  def rebuild_env(env, args=nil)

    parallel = false
    if !args.nil?
      parallel = 'true'.eql? args[:parallel]
    end

    set_env(env)

    puts "\n------------------------------------------------------------------------------------------------------------"

    # Parallel
    if parallel && (env.eql? :test)

      puts "Rebuilding the [#{env}] parallel environments..."
      begin
        run('parallel:drop')
      rescue
      end
      run('parallel:create')
      run('parallel:migrate')

      puts "\nDone with the [#{env}] parallel environments."
    else

      puts "Rebuilding the [#{env}] environment..."
      run('db:drop')
      # assert_correct_db()
      run('db:create')
      assert_correct_db()
      run('db:migrate')
      print_tables()
      assert_correct_db()
      run('db:seed')
      assert_correct_db()

      # these do not work in parallel
      puts "\nDone with [#{current_db()}] for the [#{env}] environment."
    end

    puts "------------------------------------------------------------------------------------------------------------\n"
  end


  def run(task_name)
    print "\nRunning #{task_name}..."
    Rake::Task[task_name].reenable
    Rake::Task[task_name].invoke
    print "done.\n"
  end

  def set_env(env)
    Rails.env = env.to_s
    ENV['RAILS_ENV'] = env.to_s
    ActiveRecord::Tasks::DatabaseTasks.env = env.to_s

    # This will cause the engine and configurations to be loaded.  Need this for things like the proper migrations appended by the engine
    run(:environment)
  end
end