How to structure a contract for future upgrades

Question

Imagine I have a contract I have implemented and deployed like this:

pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/utils/Counters.sol";

contract GameItem is ERC721 {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor() ERC721("GameItem", "ITM") public {
    }

    function awardItem(address player, string memory tokenURI) public returns (uint256) {
        _tokenIds.increment();

        uint256 newItemId = _tokenIds.current();
        _mint(player, newItemId);
        _setTokenURI(newItemId, tokenURI);

        return newItemId;
    }
}

After deploying the contract and people using for sometime, I feel the need to implement an auction system for these tokens...

How would I structure my solidity code to enable these upgrades without losing original data?

Answer 1

In your example, there is no restriction on who can mint tokens, so tokens are unlikely to have significant value as anyone can mint additional tokens (unless there is value in having low token IDs).

Assuming you already have this deployed, you could look at doing a migration to a V2, where the ability to mint is restricted. This would mean creating a new contract and minting tokens for the existing holders and updating your own dapp, along with services such as OpenSea to use the new version. Your existing version V1 would still exist but you would be advising holders to use V2. As for auction functionality, I would look at using services such as OpenSea or creating a contract to sell your tokens, rather than baking in to your token.

If you haven't already deployed this on mainnet, you could create an upgradeable contract (depending on your use case) using OpenZeppelin Upgrades.

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