An alternative to ERC721Enumerable and tokenOfOwnerByIndex()?

Question

I'm trying to find a way round using the ERC721Enumerable.sol extension because it essentially doubles the gas fees on minting but the tokenOfOwnerByIndex() function is a bit of an essential for what i'm doing. I basically want to get a list of all the token ids owned by a particular address as quickly and easily as possible.

Anyone have any thoughts on a workaround? Even something off-chain? I did have something going using the Etherscan API to query a wallet and then sort though results to get the tokens they own but it can be a little slow. I have also tried Moralis.io but they can take a few minutes to index onchain events which can be an issue for UX in my particular use case.

Answer 1

OZ's ERC721Enumerable has 2 functionalities basically: enumeration of tokens by owner, and enumeration of all tokens. Since you need only the enumeration by owner, you can remove from their implementation everything dealing with _allTokens and _allTokensIndex. This will probably save around half the gas costs.

Answer 2

If you develop a contract by yourself, you are able to write your own functionality.

Just create a structure which will store ids of tokens per user address:

mapping(address => uint256[]) private _tokensByAddress;

On mint a new token, transfer or burn methods calls update this dataset. It would be good to write a test suite to confirm your implementation is stable.