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Spend ERC-20 Create ERC-721

This is a technology demonstration showing a simple token usage scenario.

  1. You sell utility tokens to your customers (ICO)
  2. Your customers spend these tokens and create certificates
  3. Anybody can verify the certificates

Try the demo

Install MetaMask or other Web3-compatible browser setup, get a few Ether from a free faucet and load the demonstration website.

Demo website: https://fulldecent.github.io/spend-ERC20-create-ERC721/

How does it work

ERC-721 certificate contract — This is a standard ERC-721 contract implemented using the 0xcert template with additional functions:

  • create(bytes32 dataHash) returns (uint256) — Allows anybody to create a certificate (NFT). Causes the side effect of deducting a certain amount of money from the user, payable in ERC-20 tokens. The return value is a serial number.
  • hashForToken(uint256 tokenId) view — Allows anybody to find the data hash for a given serial number.
  • mintingPrice() view — Returns the price.
  • mintingCurrency() view — Returns the currency (ERC-20)
  • setMintingPrice(uint256) — Allows owner (see 0xcert ownable contract) to set price
  • setMintingCurrency(ERC20 contract) — Allows owner (see 0xcert ownable contract) to set currency

ERC-20 token contract — This is a standard ERC-721 contract implemented using the OpenZeppelin template for ERC-20 including Minter extension also with additional functions:

  • isSpender(address) view, addSpender(address), renounceSpender() — A new role for tracking who may spend these tokens, see OpenZeppelin roles library
  • spend(account from, uint256 value) — Allows an authorized spender to deduct money from a specific account's balance
  • mint(address to, uint256 value) — FOR DEMO PURPOSES ONLY. This implements the Minter role to allow ANYBODY to create tokens for free. This allows the demo to be used for anybody free of cost.

Deployment

When you deploy the certificate and token contracts then you will be the owner with permissions to finish the deployment.

  • Authorize the certificate contract as a spender for the tokens
  • Set the tokens as the spendable currency for the certificate

Watch deployment: https://www.youtube.com/watch?v=3SiMPZbwlR0

Contract development

I recommend saving these files on localhost and then developing using Remix IDE. Follow this process using the command line:

  1. Install remixd and smart contract dependencies

    npm install

  2. Switch into the project folder and run remixd -s .

  3. Open Remix IDE and click the connect button

  4. Develop and run the contract from Remix IDE

Attribution

This project was created by William Entriken. Thank you to Arianee for funding the development of this technology demonstration.