upgradeWorkerStep3.sol

pragma solidity ^0.4.18;

contract DB {
    uint public data;
    
    function updateData(uint _val) public {
        data = _val;
    }
}

contract Worker1 {
  address public db;

  function setN(uint _n) public {
    db.delegatecall(bytes4(keccak256("updateData(uint256)")), _n);
  }
  
  function setDB(address _addr) public {
      db = _addr;
  }
}


contract Worker2 {
  address public db;

  function setN2(uint _n) public {
    db.delegatecall(bytes4(keccak256("updateData(uint256)")), _n);
  }

  function setDB(address _addr) public {
      db = _addr;
  }
}

contract Factory {
    
    address worker;
    
    function updateWorker(address _w) public {
        worker = _w;
    }
    
    function getWorker() view public returns (address) {
        return worker;
    }
    
    function doWork(uint _val, string fnName) public {
        worker.call(bytes4(keccak256(fnName)), _val);
    }
}