📄 Adding metadata

NFTs signify ownership of a non-fungible asset on a blockchain. However, these tokens inherently lack data; to give these tokens meaningful representation, they require associated metadata. Metadata normally includes media (image or video), a name, and various other properties.

Setting up sample metadata

For the sake of simplicity, we've setup metadata for the NFT contract we just wrote. NFT metadata is just JSON data that includes a pointer to some media and some attributes. Here's what our sample metadata looks like:

{
  "image": "ipfs://QmRmuCkoz1DAobvB9fofe4RekB9sgjuy5gujDVv4u4FzSM",
  "name": "My First NFT"
}

The first field is an image that points to a location in IPFS (opens in a new tab). Most dApps that interact with NFTs recognize this data format, and will fetch the image from IPFS to render it on the frontend. We've also included a name field that apps can use for display purposes.

To save you time and money, we've uploaded this sample metadata to IPFS already. The IPFS pointer is ipfs://QmRmuCkoz1DAobvB9fofe4RekB9sgjuy5gujDVv4u4FzSM.

Adding metadata to our contract

All we need to do now is change our NFT contract to point to this metadata in its tokenURI function. Here's what the new contract will look like:

pragma solidity ^0.8.21;
 
import "erc721a/ERC721A.sol";
 
contract MyFirstFrameNFT is ERC721A {
    constructor() ERC721A("MyFirstFrameNFT", "FIRST") {}
 
    function mint(uint256 quantity) external {
        _mint(msg.sender, quantity);
    }
 
    function tokenURI(uint256) public view override returns (string memory) {
        return "ipfs://QmRmuCkoz1DAobvB9fofe4RekB9sgjuy5gujDVv4u4FzSM";
    }
}

This tokenURI function returns the same metadata for every token id. For real contracts, you'll most likely want to return different metadata for each token id.