"Branch" your database together with git

_note.md

This code is obsolete

For a much more elegant way, visit my blog.

environment.rb

# Bootstrap the Rails environment, frameworks, and default configuration
require File.join(File.dirname(__FILE__), 'boot')
require 'git_conf'

Rails::Initializer.run(:process, GitConf.new) do |config|
  # ...
end

gistfile2.builder

#!/usr/bin/env ruby
## lib/tasks/git.thor
# 
# Thor task to fully copy your master database into a new database for current branch.
# Sample usage:
# 
#   thor git:db:clone
# 
# What gets run:
# 
#   mysqladmin -u #{user} create #{target}
#   mysqldump -u #{user} #{from} | mysql -u #{user} #{target}
# 
# Limitation: only works if password authentication isn't required.
# 
class Git < Thor
  module Command
    protected

    def command(com, capture = false)
      unless capture
        system(com)
      else
        @output = %x(#{com}).chomp
      end
    end
    
    def last_command_was_success?
      $?.success?
    end
  end
  
  class Db < Thor
    include Command
    
    desc "clone", "Branch your development database"
    method_options :force => :boolean
    def clone
      require 'config/boot'
      require 'git_conf'
      config   = GitConf.new
      dbconfig = config.database_configuration["development"]
    
      if config.branched_database?
        user = dbconfig["username"]
        from = dbconfig["master-database"]
        to   = dbconfig["database"]
      
        # create the new database
        command "mysqladmin -u #{user} create #{to} 2>&1", true
      
        unless last_command_was_success?
          if @output.index('database exists')
            warn %(Database "#{to}" already exists)
            return unless options[:force]
          else
            warn @output
            return
          end
        end
      
        # clone development database
        command "mysqldump -u #{user} #{from} | mysql -u #{user} #{to}"
        puts %(Finished cloning "#{from}" to "#{to}".) if last_command_was_success?
      else
        warn "branch isn't configured for a separate database"
      end
    end
  end
end

git_conf.rb

## lib/git_conf.rb
if 'development' == RAILS_ENV
  require 'rubygems'
  require 'grit' # use "mojombo-grit" from github
  
  ## uncomment if your application is running in an environment
  ## where `git` command cannot be found in the PATH (i.e. Passenger)
  # Grit::Git.git_binary = '/usr/local/git/bin/git'
end

def Rails.repo
  @@repository ||= Grit::Repo.new(Rails.root)
end

# Adjust your environment.rb to use this subclass:
#   Rails::Initializer.run(:process, GitConf.new) do |config|
#     ...
#   end
class GitConf < Rails::Configuration
  def initialize
    super
    @branched_database = false
  end
  
  def branched_database?() @branched_database end
  
  # agument the original method in order to append
  # the branch name suffix in certain conditions
  def database_configuration
    @database_configuration ||= begin
      config = super
      if Rails.env == "development"
        head = Rails.repo.head
        branch = head && head.name
        # check if this branch has a special database
        if branch and branch != "master" and branch !~ /\W/ and branch_has_database?(branch)
          development = config["development"]
          # save original configuration
          development["master-database"] = development["database"]
          # append branch name suffix
          base_name, extension = development["database"].split(".", 2)
          development["database"] = "#{base_name}_#{branch}"
          development["database"] += ".#{extension}" if extension
          # finally, indicate that this database has branched
          @branched_database = true
        end
      end
      config
    end
  end
  
  protected
  
  def branch_has_database?(branch)
    Rails.repo.config["branch.#{branch}.database"] == "true"
  end
end