[Ethereum] ERC721 – getting the list of all token owners (all addresses)

erc-721

I have an ERC721 compliant contract with multiple NFT tokens.

I'm looking for a way to randomly select one of the token owners. Is there a way to get the current list or all token owners from ERC721 or do I need to create the mapping myself?

If creating the mapping myself, I guess I would need to add the minters address to a mapping of all owners, then whenever the token is transferred I need to update the new owner address. How do I override all the transfer functions?

Best Answer

You can try to fetch all emitted Transfer events using getPastEvents function. Based on ERC721 interface Transfer event is emitted when ownership changes.

/// @dev This emits when ownership of any NFT changes by any mechanism.
///  This event emits when NFTs are created (`from` == 0) and destroyed
///  (`to` == 0). Exception: during contract creation, any number of NFTs
///  may be created and assigned without emitting Transfer. At the time of
///  any transfer, the approved address for that NFT (if any) is reset to none.

event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);

Related Solutions

Solidity – Best Method to List All Tokens of a User

This can be achieved by the following:

Declare storage variables at the contract level

mapping(address => uint256[]) public userOwnedTokens;
mapping(uint256 => int256) public tokenIsAtIndex;

mint(tokenId) {
    // Prior minting logic from OpenZeppelin
    userOwnedTokens[msg.sender].push(tokenId);
    uint256 arrayLength = userOwnedTokens[msg.sender].length;
    tokenIsAtIndex[tokenId] = arrayLength;
}

To get all user tokens without loop, all you have to do is, this is possible as the access specifier for userOwnedTokens is public

contractInstance.methods.userOwnedTokens.call(address) // THIS WILL RETURN AN ARRAY OF TOKEN IDs

In case of transfer of tokens, change tokenIsAtIndex[tokenId] to -1

transfer(from, to, tokenId) {
    // Transfer logic
    uint256 tokenIndex = tokenIsAtIndex[tokenId];
    userOwnedTokens[from][tokenIndex] = 000; // TO DENOTE THAT THE TOKEN HAS BEEN TRANSFERRED, YOU CAN USE ANY OTHER NUMBER
 }

Next time when userOwnedTokens is called you can keep a check wherever the tokenId is 000, those tokens have already been transferred and you can decide not to show it to the user on the frontend.

I hope it helps!!!!!

ERC721 – Smart Contract Transfer Tokens as the Contract Owners

The EIP-721 provides a function isApprovedForAll(address owner, address operator)

Query if an address is an authorized operator for another address

That function can be used enable a special address to always be authorized to operate on the NFTs.

Best Answer

Related Solutions

Solidity – Best Method to List All Tokens of a User

ERC721 – Smart Contract Transfer Tokens as the Contract Owners

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