从合约中读取 NFT 的 JSON 元数据

Question

are there any legal ways to get details about NFT metadata from inside its contract? Let say I have NFT with id 1, which metadata is stored on IPFS and it has rarity attribute 10. Is it possible to fetch that data from inside contract? Or the only way is to introduce rarity attribute on contract and then populate it later with 3rd party utility?

Answer 1

you can technically fetch data from the contract if there is an oracle service built specifically for fetching data from ipfs. however, this is too expensive and unnecessary service so there is no oracle service for this.

Instead, we fetch the data from Ipfs off-chain from front end. We store the tokenUri inside the contract. On the front end, we get the tokenUri and fetch data from Ipfs using this tokenUri.

 const tokenURI = await contract.tokenURI(tokenId);
 const metaRes = await fetch(tokenURI);

Answer 2

Most of the NFTs with metadata is an implementation of ERC721Metadata interface , which has the following method:

    /// @notice A distinct Uniform Resource Identifier (URI) for a given asset.
    /// @dev Throws if `_tokenId` is not a valid NFT. URIs are defined in RFC
    ///  3986. The URI may point to a JSON file that conforms to the "ERC721
    ///  Metadata JSON Schema".
    function tokenURI(uint256 _tokenId) external view returns (string);

This method, tokenURI returns URI of metadata for given tokenId .

Metadata attributes usually follows opensea metadata standards