code: def connect_database(url):
      
      db = _connect_database(url)
      db.copy = lambda: _connect_database(url)
      return db
docs: create database object by url
  
      mysql:
          mysql+type://user:passwd@host:port/database
      sqlite:
          # relative path
          sqlite+type:///path/to/database.db
          # absolute path
          sqlite+type:////path/to/database.db
          # memory database
          sqlite+type://
      mongodb:
          mongodb+type://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database][?options]]
          more: http://docs.mongodb.org/manual/reference/connection-string/
      sqlalchemy:
          sqlalchemy+postgresql+type://user:passwd@host:port/database
          sqlalchemy+mysql+mysqlconnector+type://user:passwd@host:port/database
          more: http://docs.sqlalchemy.org/en/rel_0_9/core/engines.html
      redis:
          redis+taskdb://host:port/db
      elasticsearch:
          elasticsearch+type://host:port/?index=pyspider
      local:
          local+projectdb://filepath,filepath
  
      type:
          taskdb
          projectdb
          resultdb