# Example of implementation of EIP 4906 metadata updates

By [0xCardie](https://paragraph.com/@0xcardie) · 2023-03-26

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EIP 4096 has an interesting method of updating your metadata with events, more details here.

[https://eips.ethereum.org/EIPS/eip-4906](https://eips.ethereum.org/EIPS/eip-4906)

So lets see how to implement it with an example. First you need to create a file with interface that has this code in it

    pragma solidity ^0.8.0;
    
    import "@openzeppelin/contracts/utils/introspection/IERC165.sol";
    
    /// @title EIP-721 Metadata Update Extension
    interface IERC4906 is IERC165 {
        /// @dev This event emits when the metadata of a token is changed.
        /// Third-party platforms such as NFT marketplaces can listen to
        /// the event and auto-update the tokens in their apps.
        event MetadataUpdate(uint256 _tokenId);
        /// @dev This event emits when the metadata of a range of tokens is changed.
        /// So that the third-party platforms such as NFT market could
        /// timely update the images and related attributes of the NFTs.
        event BatchMetadataUpdate(uint256 _fromTokenId, uint256 _toTokenId);
    }
    

then we can implement that interface like example below (we also need to use supportsInterface function) and call our event **BatchMetadataUpdate** in the case of updating of **\_baseTokenURI** as this means all NFTs have new URIs and probably new metadata.

    pragma solidity ^0.8.0;
    
    import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
    import "./IERC4906.sol";
    
    contract ERC4906 is ERC721, IERC4906 {
    
    string private _baseTokenURI = "some URI"
    
        constructor(string memory name_, string memory symbol_) ERC721(name_, symbol_) {
        }
    
        function supportsInterface(
            bytes4 interfaceId
        ) public view virtual override(ERC721A, IERC165) returns (bool) {
            return super.supportsInterface(interfaceId);
        }
    
        function setBaseURI(string calldata baseURI) external onlyOwner {
            emit BatchMetadataUpdate(1, type(uint256).max);
            _baseTokenURI = baseURI;
        }
    }
    

One of the good things is that this EIP has been supported by Open Sea, which means it should be useful and standardized across industry.

[https://docs.opensea.io/docs/metadata-standards#metadata-updates](https://docs.opensea.io/docs/metadata-standards#metadata-updates)

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*Originally published on [0xCardie](https://paragraph.com/@0xcardie/example-of-implementation-of-eip-4906-metadata-updates)*