SQLite & rake-based Git & Rails database branching, see http://tinyurl.com/a7e6jo

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

git.rake

#!/usr/bin/env ruby
## lib/tasks/git.rake
# 
# Rake task to fully copy your master database into a new database for current branch.
# Sample usage:
# 
#   rake git:db:clone
# 
# What gets run:
# 
#   cp #{from} #{target}
# 
namespace :git do
  namespace :db do
    desc "Branch your development database"
    task :clone => :environment do
      require 'fileutils'
      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"]
        
        FileUtils.cp(from, to)
      else
        warn "branch isn't configured for a separate database"
      end
    end
  end
end

git_conf.rb

## lib/git_conf.rb
# Tell a branch to have its own database with:
#   git config branch.#{branch_name}.database true
# Clone from master with rake git:db:clone
require 'rubygems'
require 'grit' # "mojombo-grit" gem from github

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