Keep migrations straight when you (a) have a lot of them or (b) use data_migration plugin

incoming_migration_check.rake

namespace :db do
  namespace :migrate do
    desc "Do you need to run db:migrate or db:data:migrate? `rake db:migrate:incoming_check'[SHA1 RANGE]'`"
    task :incoming_check, :git_refs, :needs => :environment do |task, args|
      # User story:
      # as a developer, I should be able to see what migrations have changed
      # in a series of commits -- what new ones and what old ones - so I can know
      # what migration commands I need to run (rake db:migrate,
      # rake db:data:migrate PATH=..., (if you're using the data_migration plugin!) or maybe just alert you that
      # you should complain to your fellow devs because someone changed an old migration!)
      #
      # Assumes you're using git. This is github after all.
      #
      # Example:
      # $ git pull
      # ......
      # 931ab31..304eee2  master -> master
      # $ rake db:migrate:incoming_check"[931ab31..304eee2]"
      # will return nothing if there are no migrations affected by that git sha1 range
      # will tell you about new migrations or old migrations as appropriate
      
      db_modified_files = `git diff --numstat #{args[:git_refs]} | cut -f3 - | grep db/`

      db_modified_files.each do |current_file|
        if current_file =~ /db\/.+\/(\d+)_.+\.rb/  # ok, it's a migration file (vs schema or something)
          migration_version = $~[1]
          res = ActiveRecord::Base.connection.execute("select COUNT(*) from schema_migrations WHERE version='#{migration_version}'")
          
          if res.kind_of? Mysql::Result
            # make MySQL results look like the results we get from sqlite. RPW 09-13-2010
            out = []
            res.each {|r| out << r}
            res = out
          end
          
          if res[0][0] == 0
            puts "NEW MIGRATION: #{current_file}"
          else
            puts "OLD MIGRATION, CHANGED: #{current_file}"
          end
        end
      end
    end
  end
end