# Get & Set Value 2.0 | Web3.0 dApp Dev 0x05

By [Web3dAppDevCamp](https://paragraph.com/@apecoder) · 2021-11-23

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In our 1.0 version, we created a simple Get & Set value dApp and its contract and deploy that onto Github-Pages.

Now, we can upgrade the 1.0 version. It will become much cooler with economic model!

0x01 Make contracts folder sub Repo of the project
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In the repo, we can see that the contracts folder actually stores another repo. Here we used the `submodule` feature of git.

For smart contract, the benefit of doing this is that for the same dApp, we may have different contract versions. For NFT project, we may have the regular version, whitelist version, upgradeable version and etc. If we set contracts as submodule, we will be able to switch contracts inside the folder directly.

Here are some git commands for `submodule`:

    # add submodule for this folder
    git submodule add submodule-repository-URL
    # example:
    # git submodule add https://github.com/leeduckgo/set-purpose-contracts.git
    
    # clone the submodule when cloning repo
    git clone --recurse-submodules repository-URL
    
    # manually clone specified submodules
    git submodule update --init folder-path
    # example:
    # git submodule update packages/hardhat/contracts --init
    

0x02 add access control to setPurpose
-------------------------------------

On basis of `PurposeHandler`, we can use `require` statements to add access control to `setPurpose` . When the caller of the contract is not the assigned `owner` in the constructor function, an error will occur and the following code will not be executed.

    pragma solidity >=0.8.0 <0.9.0;
    //SPDX-License-Identifier: MIT
    
    import "hardhat/console.sol";
    
    contract PurposeHandler {
    
      //event SetPurpose(address sender, string purpose);
    
      string public purpose = "Building Unstoppable Apps";
      address public owner = 0x7EF99B0E5bEb8ae42DbF126B40b87410a440a32a;
      // replace with your own address
    
      constructor() {
    
        // owner = msg.sender;
      }
    
      function setPurpose(string memory newPurpose) public {
          // about msg.sender:
          // https://cryptozombies.io/en/lesson/2/chapter/3
          // about require:
          // https://cryptozombies.io/en/lesson/2/chapter/4
          require( msg.sender == owner, "NOT THE OWNER!");
    
          purpose = newPurpose;
          console.log(msg.sender,"set purpose to",purpose);
          //emit SetPurpose(msg.sender, purpose);
      }
    }
    

> \*\*TIPS: \*\*
> 
> More about msg.sender: [https://cryptozombies.io/en/lesson/2/chapter/3](https://cryptozombies.io/en/lesson/2/chapter/3)
> 
> More about require: [https://cryptozombies.io/en/lesson/2/chapter/4](https://cryptozombies.io/en/lesson/2/chapter/4)

Go back to set-purpose root directory. Start local network, deploy the contract, and start the dApp:

    export SKIP_PREFLIGHT_CHECK=true # config environment variable
    yarn chain # Start local blockchain network
    yarn deploy # Deploy contract
    yarn start # run dApp
    

image-20211029132355937

Open up `http://localhost:3000` in browser.

When Owner is making transaction:

set\_purpose\_v0x02

When address other that Owner is making transaction:

set\_purpose\_v0x02-wrong

> TIPS：
> 
> If address have errors related to Nonce, just reset the Nonce:
> 
> Metamask > Settings > Advanced > Reset Account

Authors:

[leeduckgo](https://noncegeek.com/namecards/leeduckgo.svg?display=iframe)

[msfew](https://noncegeek.com/namecards/msfew.svg?display=iframe)

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*Originally published on [Web3dAppDevCamp](https://paragraph.com/@apecoder/get-set-value-2-0-web3-0-dapp-dev-0x05)*