Save and restore the state of your Rails development and test databases as you work on different branches

post-checkout

#!/usr/bin/env ruby

require 'yaml'

# If this was a branch checkout
if ARGV[2] == '1'
  def dump(database_name, branch_name)
    print "Saving state of #{database_name} on '#{branch_name}' branch..."

    if system(%[pg_dump -c -f "#{@dump_folder}/#{database_name}-#{branch_name}" #{database_name}])
      print "done!\n"
      true
    else
      print "failed!\n"
      false
    end
  end

  def restore(database_name, path)
    system(%[psql #{database_name} < #{path} > /dev/null 2>&1])
  end

  def branches_from_refhead(ref)
    `git show-ref --heads | grep #{ref} | awk '{print $2}'`.split("\n").map{ |b| b.sub(/^refs\/heads\//, '') }
  end

  # Get the current (destination) branch
  @destination_branch = `git rev-parse --abbrev-ref HEAD`.strip

  # Since we're just given a commit ID referencing the branch head we're coming from,
  # it could be at the head of multiple branches. We can assume the source isn't the same as the
  # destination branch, so we can remove that immediately.
  @source_branches = branches_from_refhead(ARGV[0]).reject{ |b| b == @destination_branch }

  @project_root = %x[git rev-parse --show-toplevel].strip
  @dump_folder = "#{@project_root}/.db_branch_dumps"

  # Load Rails DB config and grab database name
  rails_db_config = YAML.load_file("#{@project_root}/config/database.yml")
  dev_database_name = rails_db_config['development']['database']
  test_database_name = rails_db_config['test']['database']

  # Ensure dump directory exists
  unless Dir.exists?(@dump_folder)
    Dir.mkdir @dump_folder
  end

  # Don't do anything if the source and destination branches are the same or nonexistent
  unless @source_branches.include?(@destination_branch) || @source_branches.empty? || (@source_branches | [@destination_branch]).any?{ |b| b == '' }
    # Dump database for source branches
    if @source_branches.all? { |branch| dump(dev_database_name, branch) }
      # Restore dump from this branch, if it exists
      dump_path = "#{@dump_folder}/#{dev_database_name}-#{@destination_branch}"

      if File.exists?(dump_path)
        print "Restoring #{dev_database_name} to its previous state on this branch..."

        if restore(dev_database_name, dump_path)
          print "done!\n"

          # If we have a structure.sql file, restore that to the test database,
          # otherwise fall back to rake
          structure_sql = File.join(@project_root, 'db', 'structure.sql')

          if File.exists?(structure_sql)
            print "Restoring test database from structure.sql..."

            print restore(test_database_name, structure_sql) ? "done!\n" : "failed!\n"
          else
            print "Preparing test database..."

            system %[rake db:test:prepare]

            print "done!\n"
          end
        else
          print "failed!\n"
        end
      else
        print "No DB dump for #{dev_database_name} on the '#{@destination_branch}' branch was found!\n"
        print "The state of your database has been saved for when you return to the '#{@source_branches.join('\' or \'')}' branch, but its current state has been left unchanged.  You are now free to make changes to it that are specific to this branch, and they will be saved when you checkout a different branch, then restored when you checkout this one again.\n"
      end
    else
      print "Failed to dump database. Halting.\n"
    end
  end
end