This task originally written by Stephen Chu.

If you are using migrations on a large team, migration conflicts can and do occur. To help avoid conflicts you can add the following task to your codebase and run it after updating and before checking in (hopefully in your commit task).

namespace :db do
  namespace :migration do
    desc "After downloading migrations from server, check to see if we have conflicting migration numbers."
    task :conflict do
      existing_migration_numbers = []
      Dir.entries("#{RAILS_ROOT}/db/migrate").each do |entry|
        migration_number = entry.scan(/^\d+/).first
        next if migration_number.nil?
        if existing_migration_numbers.include? migration_number
          raise ArgumentError, "Migration #{migration_number} is already checked in on the server. Verify your migration numbers."
        end
        existing_migration_numbers << migration_number
      end    
    end
  end
end