How to transfer NFT metadata from IPFs to smart contracts

When  

Millionaire’s Mining Club

  When first introduced ,NFT  Metadata is stored in  IPFS  On . At that time, it seemed to be the right choice , But later  IPFS  Start limiting its flexibility , From then on, exploration will  NFT  Metadata is stored in smart contracts .

What is? NFT Metadata

according to  

ERC-721 NFT

  standard ,NFT  Can have optional  

tokenURI

  function .

tokenURI

  There is one  

tokenId

  The input of , And return a string  

URI

, It contains descriptions  NFT  Additional metadata for . This  

tokenURI

  image  

OpenSea

  How can such a platform find information about  NFT  Image 、 attribute 、 Statistics 、 Details, etc .

Let's look at an example ：

{
 "name": "Founders Edition",
 "description": "Founders Edition Nifty Miner",
 "external_url": "https://miningclub.app/token/0",
 "image": "https://gateway.pinata.cloud/ipfs/QmTyeUQzwCnAPx9ZruQA9isdHP4YDdmbr1boqDSXFJGBbp/founders-electric-blue+.png",
 "background_color": "ffffff",
 "attributes": [
 {
 "trait_type": "Mint Number",
 "value": 1,
 "display_type": "number"
 },
 {
 "trait_type": "Edition",
 "value": "Founders"
 },
 {
 "trait_type": "Rarity",
 "value": "Ultra Rare"
 },
 {
 "trait_type": "Highlight",
 "value": "Electric Blue"
 },
 {
 "trait_type": "Quality",
 "value": "Perfect"
 }
 ]
}


This is the description  OpenSea  On  

Founders Edition NFT（tokenId  by  0）

Metadata .

Why store metadata in  IPFS  On ？

Initially, metadata was stored in  IPFS  On , This is the industry standard , Is the way most projects store metadata . This usually applies to most with immutability  NFTS（ Or unchanged  NFT） Project .

Pinata

  stay  IPFS  There is a  

https URI

  wrapper , by  OpenSea  Query provided  NFT  A simple method of metadata .

Why not  IPFS  Store metadata on ？

With  Millionaire’s Mining Club,IPFS  Has become a limitation , Every time  NFT  When the data changes , Must push a new set of metadata to  IPFS.

Inquire about  IPFS  It could be very slow .

IPFS  You also need one that is always on and connected to  IPFS  Network machine to provide documents , It usually involves things like  

Pinata

  Such a fixed service . Every time the  IPFS  When making changes ,

Pinata

  It must also be updated .

Nifty Miner NFT  Need more flexibility , You need to be able to update metadata immediately and trigger updates from the smart contract itself . Use  IPFS, This quickly becomes complicated .

How to store metadata in smart contracts

Smart contracts know about  NFT  All the information about , And you can easily update properties . It makes sense to find a solution that also stores metadata in smart contracts . In addition to the usual standard  URI, And data  URI.

Example data  URI：

data:application/json;base64,eyJoZWxsbyI6IndvcmxkIn0=

This data  URI  The type of  

application/json

, So is it  

base64

  Coded . 

base64

  Coding for  

OpenSea

  analysis  

URI

  Very important .

This data  URI  The content is ：

{"hello":"world"}


The limitation of storing metadata in smart contracts

The first limitation is  URI  Size . URI  Best practices for are limited to  2,000  Characters . So it's best to keep under this limit as much as possible . If  NFT  Metadata exceeds this limit , be  Data URI  The solution will not work .

Now a large amount of string data must be stored in smart contracts . This will increase the cost of deploying smart contracts , But more importantly, it will make smart contracts face more than the size of smart contracts  24KB  The danger of restriction .

Metadata changes may require redeployment of smart contracts .

Solution

The solution is to deploy a separate  

JsonMetadata

  Intelligent contract . This will make the main  NFT  Smart contracts remain huge , Keep at  24KB  Within the limits of .

Then you can learn from the master  NFT  Smart contract calls  

JsonMetadata

  Method and return data  URI.

This is a  

JsonMetadata

  A small fragment of smart contract .

import "@openzeppelin/contracts-upgradeable/access/AccessControlUpgradeable.sol";
import "@openzeppelin/contracts/utils/Base64.sol";
contract JsonMetadata is AccessControlUpgradeable {
 string public _baseUri;
 string constant _dataUri = "data:application/json;base64,";
 function getVipCardUri() public view returns (string memory) {
 bytes memory json = abi.encodePacked(
 '{"description":"VIP Card","external_url":"',
 _baseUri,
 'vip-card.png","image":"',
 _baseUri,
 'vip-card.png","animation_url":"',
 _baseUri,
 'vip-card.glb","name":"VIP Card","background_color":"ffffff","attributes":[{"trait_type":"Status","value":"VIP"},{"trait_type":"Access","value":"Whitelist"}]}'
 );
 return string(abi.encodePacked(_dataUri, Base64.encode(json)));
 }
}


summary

stay  IPFS  On storage  NFT  Metadata limits our dynamics  NFT. Metadata needs to be consistent with  NFT  Same dynamic . data  URI  Provides a way to  NFT  Solutions where metadata is stored directly in smart contracts .