I am using openzeppelin erc721 library to create an NFT and need to list all the tokens of a user. The most obvious way is to iterate through all the tokens in the contract and check if the owner of the token is same as the address I have sent.

function tokensOfOwner(address _owner) external view returns(uint256[] ownerTokens) {
    uint256 tokenCount = balanceOf(_owner);

    if (tokenCount == 0) {
        // Return an empty array
        return new uint256[](0);
    } else {
        uint256[] memory result = new uint256[](tokenCount);
        uint256 totalCats = totalSupply();
        uint256 resultIndex = 0;

        // We count on the fact that all cats have IDs starting at 1 and increasing
        // sequentially up to the totalCat count.
        uint256 catId;

        for (catId = 1; catId <= totalCats; catId++) {
            if (kittyIndexToOwner[catId] == _owner) {
                result[resultIndex] = catId;

        return result;

Link to this solution

Another solution that I am thinking of implementing is to have a mapping where I map the user address to an array or another mapping which includes all the tokens the user owns. Upon transferring the token to another address, I would need to remove the token from seller list and add it to buyers list. This solution sounds more reasonable but I dont know how cost efficient it will be. What are the disadvantages of this method?

  • 2
    Whatever you do, try to stay away from loops. They are consuming gas. Try to solve these kind of problems off-chain if you can. May 5, 2021 at 19:08
  • take look at this docs.openzeppelin.com/contracts/2.x/api/token/… and see how they implement this method _tokensOfOwner(owner) return all tokens of owner in ERC721 is not a good idea, it is a "NFT" and such a thing you trying to do will only work for a very low number of tokens
    – Majd TL
    May 7, 2021 at 13:06
  • @MajdTL then can you elaborate how properly to list all the NFT, like for marketplace but without the need of centralisation server like opensea? because it is ridiculous when u can't display the list items. Feb 8, 2022 at 0:59
  • 1
    @MiratCanBayrak external view won't use gas, so actually when it's view function, always use loops if possible. Feb 8, 2022 at 1:01
  • If you just want the data offChain to view it and it is not needed to be used by other smart contract then take a look at the Graph. it is a decentralized protocol for indexing and querying data from blockchains. @DellWatson
    – Majd TL
    Feb 8, 2022 at 12:15

3 Answers 3


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
    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];

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!!!!!

  • Dont really get what is tokenIsAtIndex used for when you just call methods.userOwnedTokens.call(address) tokenIsAtIndex dont have anything with that part?
    – Blissful
    Sep 29, 2021 at 11:36
  • 1
    I don't know why this answer get accepted, definitely wrong when I tried it. userOwnedTokens is on array which userOwnedTokens require index so it will be userOwnedTokens(address, uint256) which make contractInstance.methods.userOwnedTokens.call(address) -> INVALID, from logic itself is already wrong. Feb 8, 2022 at 0:24

In the first answer, as you declare "mapping(address => uint256[]) public userOwnedTokens", it expects an address and an uint (position in the array) in the call function. That was my experience.

Based on suggestion made by @dwardu/@hack3r_0m, extend ERC721Enumerable, the following code worked for me, without worries with mappings and indexes:

function getTokenIds(address _owner) public view returns (uint[] memory) {
        uint[] memory _tokensOfOwner = new uint[](ERC721.balanceOf(_owner));
        uint i;

        for (i=0;i<ERC721.balanceOf(_owner);i++){
            _tokensOfOwner[i] = ERC721Enumerable.tokenOfOwnerByIndex(_owner, i);
        return (_tokensOfOwner);

As you’re already extending OpenZeppelin’s ERC721 contract, simply extend ERC721Enumerable too, and you may then enumerate user’s tokens by calling tokenOfOwnerByIndex(user, index) for index = 0, 1, 2, …, balanceOf(user) - 1.

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