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Building a Scalable NFT Marketplace on Ethereum with Polygon

Nader Dabit
Web and mobile developer specializing in cross-platform, cloud-enabled, and Web3 application development.
Updated on ・22 min read

Building a digital marketplace with Next.js, Tailwind, Solidity, Hardhat, Ethers.js, IPFS, and Polygon

To view the video course for this tutorial, click here

In my last end to end Ethereum tutorial, The Complete Guide to Full Stack Ethereum Development I introduced how to build a basic app on Ethereum using modern tooling like Hardhat and Ethers.js.

One thing that has become apparent over the past few months is how quickly Ethereum scaling solutions like Polygon, Arbitrum, and Optimism are gaining momentum and adoption. These technologies enable developers to build the same applications they would directly on Ethereum with the added benefits of lower gas costs and faster transaction speeds among other things.

Because of the value proposition that these solutions offer combined with the general lack of existing content, I will be building out various example projects and tutorials for full stack applications using these various Ethereum scaling solutions, starting with this one on Polygon.

To view the final source code for this project, visit this repo

Prerequisites

To be successful in this guide, you must have the following:

  1. Node.js installed on your machine
  2. Metamask wallet extension installed as a browser extension

The stack

In this guide, we will build out a full stack application using:

Ethereum Layer - Polygon
Web application framework - Next.js
Solidity development environment - Hardhat
File Storage - IPFS
Ethereum Web Client Library - Ethers.js

Though it will not be part of this guide (coming in a separate post), we will look at how to build a more robust API layer using The Graph Protocol to get around limitations in the data access patterns provided by the native blockchain layer.

About the project

The project that we will be building will be Metaverse Marketplace - a digital marketplace.

Metaverse Marketplace

When a user puts an item for sale, the ownership of the item will be transferred from the creator to the marketplace.

When a user purchases an item, the purchase price will be transferred from the buyer to the seller and the item will be transferred from the marketplace to the buyer.

The marketplace owner will be able to set a listing fee. This fee will be taken from the seller and transferred to the contract owner upon completion of any sale, enabling the owner of the marketplace to earn recurring revenue from any sale transacted in the marketplace.

The marketplace logic will consist of two smart contracts:

NFT Contract - This contract allows users to mint unique digital assets.

Marketplace Contract - This contract allows users to put their digital assets for sale on an open market.

I believe this is a good project because the tools, techniques, and ideas we will be working with lay the foundation for many other types of applications on this stack – dealing with things like payments, commissions, and transfers of ownership on the contract level as well as how a client-side application would use this smart contract to build a performant and nice-looking user interface.

In addition to the smart contract, I'll also show you how to build a subgraph to make the querying of data from the smart contract more flexible and efficient. As you will see, creating views on data sets and enabling various and performant data access patterns is hard to do directly from a smart contract. The Graph makes this much easier.

About Polygon

From the docs:

"Polygon is a protocol and a framework for building and connecting Ethereum-compatible blockchain networks. Aggregating scalable solutions on Ethereum supporting a multi-chain Ethereum ecosystem."

Polygon is about 10x faster than Ethereum & yet transactions are more than 10x cheaper.

Ok cool, but what does all that mean?

To me it means that I can use the same knowledge, tools, and technologies I have been using to build apps on Ethereum to build apps that are faster and cheaper for users, providing not only a better user experience but also opening the door for many types of applications that just would not be feasible to be built directly on Ethereum.

As mentioned before, there are many other Ethereum scaling solutions such as Arbitrumand Optimism that are also in a similar space. Most of these scaling solutions have technical differences and fall into various categories like sidechains , layer 2s, and state channels.

Polygon recently rebranded from Matic so you will also see the word Matic used interchangeably when referring to various parts of their ecosystem because the name still is being used in various places, like their token and network names.

To learn more about Polygon, check out this post as well as their documentation here.

Now that we have an overview of the project and related technologies, let's start building!

Project setup

To get started, we'll create a new Next.js app. To do so, open your terminal. Create or change into a new empty directory and run the following command:

npx create-next-app digital-marketplace
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Next, change into the new directory and install the dependencies:

cd digital-marketplace

npm install ethers hardhat @nomiclabs/hardhat-waffle \
ethereum-waffle chai @nomiclabs/hardhat-ethers \
web3modal @openzeppelin/contracts ipfs-http-client \
axios
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Setting up Tailwind CSS

We'll be using Tailwind CSS for styling, we we will set that up in this step.

Tailwind is a utility-first CSS framework that makes it easy to add styling and create good looking websites without a lot of work.

Next, install the Tailwind dependencies:

npm install -D tailwindcss@latest postcss@latest autoprefixer@latest
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Next, we will create the configuration files needed for Tailwind to work with Next.js (tailwind.config.js and postcss.config.js) by running the following command:

npx tailwindcss init -p
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Finally, delete the code in styles/globals.css and update it with the following:

@tailwind base;
@tailwind components;
@tailwind utilities;
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Configuring Hardhat

Next, initialize a new Hardhat development environment from the root of your project:

npx hardhat

? What do you want to do? Create a sample project
? Hardhat project root: <Choose default path>
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Now you should see the following files and folders created for you in your root directory:

hardhat.config.js - The entirety of your Hardhat setup (i.e. your config, plugins, and custom tasks) is contained in this file.
scripts - A folder containing a script named sample-script.js that will deploy your smart contract when executed
test - A folder containing an example testing script
contracts - A folder holding an example Solidity smart contract

Next, update the configuration at hardhat.config.js with the following:

View the gist here

/* hardhat.config.js */
require("@nomiclabs/hardhat-waffle")
const fs = require('fs')
const privateKey = fs.readFileSync(".secret").toString().trim() || "01234567890123456789"

module.exports = {
  defaultNetwork: "hardhat",
  networks: {
    hardhat: {
      chainId: 1337
    },
    mumbai: {
      url: "https://rpc-mumbai.matic.today",
      accounts: [privateKey]
    }
  },
  solidity: {
    version: "0.8.4",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200
      }
    }
  }
}
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In this configuration, we've configured the local Hardhat development environment as well as the Mumbai testnet.

You can read more about both Matic networks here.

Next, create a file named .secret at the root of your project. For now, we will leave this file empty. Later on, we will populate it with a test wallet private key that will hold some Matic tokens that we will get from the Matic testnet faucet.

Be sure to never commit any private keys to Git. To be extra safe, consider storing these values in temporary environment variables when working with wallets that contain real tokens. To omit from Git, add .secret to your .gitignore file.

Smart Contracts

Next, we'll create our smart contracts! We'll start with the NFT contract for the unique digital assets.

Create a new file in the contracts directory named NFT.sol. Here, add the following code:

View the gist here

// contracts/NFT.sol
// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity ^0.8.3;

import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

import "hardhat/console.sol";

contract NFT is ERC721URIStorage {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;
    address contractAddress;

    constructor(address marketplaceAddress) ERC721("Metaverse Tokens", "METT") {
        contractAddress = marketplaceAddress;
    }

    function createToken(string memory tokenURI) public returns (uint) {
        _tokenIds.increment();
        uint256 newItemId = _tokenIds.current();

        _mint(msg.sender, newItemId);
        _setTokenURI(newItemId, tokenURI);
        setApprovalForAll(contractAddress, true);
        return newItemId;
    }
}
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This is a pretty straightforward NFT smart contract that allows users to mint unique digital assets and have ownership of them.

In this contract we are inheriting from the ERC721 standard implemented by OpenZepplin

Next, we'll create the contract for the Marketplace. This is a much larger smart contract. I've done my best to document what each function is doing.

Create a new file in the contracts directory named Market.sol:

View the gist here

// contracts/Market.sol
// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity ^0.8.3;

import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

import "hardhat/console.sol";

contract NFTMarket is ReentrancyGuard {
  using Counters for Counters.Counter;
  Counters.Counter private _itemIds;
  Counters.Counter private _itemsSold;

  address payable owner;
  uint256 listingPrice = 0.025 ether;

  constructor() {
    owner = payable(msg.sender);
  }

  struct MarketItem {
    uint itemId;
    address nftContract;
    uint256 tokenId;
    address payable seller;
    address payable owner;
    uint256 price;
    bool sold;
  }

  mapping(uint256 => MarketItem) private idToMarketItem;

  event MarketItemCreated (
    uint indexed itemId,
    address indexed nftContract,
    uint256 indexed tokenId,
    address seller,
    address owner,
    uint256 price,
    bool sold
  );

  /* Returns the listing price of the contract */
  function getListingPrice() public view returns (uint256) {
    return listingPrice;
  }

  /* Places an item for sale on the marketplace */
  function createMarketItem(
    address nftContract,
    uint256 tokenId,
    uint256 price
  ) public payable nonReentrant {
    require(price > 0, "Price must be at least 1 wei");
    require(msg.value == listingPrice, "Price must be equal to listing price");

    _itemIds.increment();
    uint256 itemId = _itemIds.current();

    idToMarketItem[itemId] =  MarketItem(
      itemId,
      nftContract,
      tokenId,
      payable(msg.sender),
      payable(address(0)),
      price,
      false
    );

    IERC721(nftContract).transferFrom(msg.sender, address(this), tokenId);

    emit MarketItemCreated(
      itemId,
      nftContract,
      tokenId,
      msg.sender,
      address(0),
      price,
      false
    );
  }

  /* Creates the sale of a marketplace item */
  /* Transfers ownership of the item, as well as funds between parties */
  function createMarketSale(
    address nftContract,
    uint256 itemId
    ) public payable nonReentrant {
    uint price = idToMarketItem[itemId].price;
    uint tokenId = idToMarketItem[itemId].tokenId;
    require(msg.value == price, "Please submit the asking price in order to complete the purchase");

    idToMarketItem[itemId].seller.transfer(msg.value);
    IERC721(nftContract).transferFrom(address(this), msg.sender, tokenId);
    idToMarketItem[itemId].owner = payable(msg.sender);
    idToMarketItem[itemId].sold = true;
    _itemsSold.increment();
    payable(owner).transfer(listingPrice);
  }

  /* Returns all unsold market items */
  function fetchMarketItems() public view returns (MarketItem[] memory) {
    uint itemCount = _itemIds.current();
    uint unsoldItemCount = _itemIds.current() - _itemsSold.current();
    uint currentIndex = 0;

    MarketItem[] memory items = new MarketItem[](unsoldItemCount);
    for (uint i = 0; i < itemCount; i++) {
      if (idToMarketItem[i + 1].owner == address(0)) {
        uint currentId = i + 1;
        MarketItem storage currentItem = idToMarketItem[currentId];
        items[currentIndex] = currentItem;
        currentIndex += 1;
      }
    }
    return items;
  }

  /* Returns only items that a user has purchased */
  function fetchMyNFTs() public view returns (MarketItem[] memory) {
    uint totalItemCount = _itemIds.current();
    uint itemCount = 0;
    uint currentIndex = 0;

    for (uint i = 0; i < totalItemCount; i++) {
      if (idToMarketItem[i + 1].owner == msg.sender) {
        itemCount += 1;
      }
    }

    MarketItem[] memory items = new MarketItem[](itemCount);
    for (uint i = 0; i < totalItemCount; i++) {
      if (idToMarketItem[i + 1].owner == msg.sender) {
        uint currentId = i + 1;
        MarketItem storage currentItem = idToMarketItem[currentId];
        items[currentIndex] = currentItem;
        currentIndex += 1;
      }
    }
    return items;
  }

  /* Returns only items a user has created */
  function fetchItemsCreated() public view returns (MarketItem[] memory) {
    uint totalItemCount = _itemIds.current();
    uint itemCount = 0;
    uint currentIndex = 0;

    for (uint i = 0; i < totalItemCount; i++) {
      if (idToMarketItem[i + 1].seller == msg.sender) {
        itemCount += 1;
      }
    }

    MarketItem[] memory items = new MarketItem[](itemCount);
    for (uint i = 0; i < totalItemCount; i++) {
      if (idToMarketItem[i + 1].seller == msg.sender) {
        uint currentId = i + 1;
        MarketItem storage currentItem = idToMarketItem[currentId];
        items[currentIndex] = currentItem;
        currentIndex += 1;
      }
    }
    return items;
  }
}
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Now the smart contract code and environment is complete and we can try testing it out.

To do so, we can create a local test to run through much of the functionality, like minting a token, putting it up for sale, selling it to a user, and querying for tokens.

To create the test, open test/sample-test.js and update it with the following code:

View the gist here

/* test/sample-test.js */
describe("NFTMarket", function() {
  it("Should create and execute market sales", async function() {
    /* deploy the marketplace */
    const Market = await ethers.getContractFactory("NFTMarket")
    const market = await Market.deploy()
    await market.deployed()
    const marketAddress = market.address

    /* deploy the NFT contract */
    const NFT = await ethers.getContractFactory("NFT")
    const nft = await NFT.deploy(marketAddress)
    await nft.deployed()
    const nftContractAddress = nft.address

    let listingPrice = await market.getListingPrice()
    listingPrice = listingPrice.toString()

    const auctionPrice = ethers.utils.parseUnits('1', 'ether')

    /* create two tokens */
    await nft.createToken("https://www.mytokenlocation.com")
    await nft.createToken("https://www.mytokenlocation2.com")

    /* put both tokens for sale */
    await market.createMarketItem(nftContractAddress, 1, auctionPrice, { value: listingPrice })
    await market.createMarketItem(nftContractAddress, 2, auctionPrice, { value: listingPrice })

    const [_, buyerAddress] = await ethers.getSigners()

    /* execute sale of token to another user */
    await market.connect(buyerAddress).createMarketSale(nftContractAddress, 1, { value: auctionPrice})

    /* query for and return the unsold items */
    items = await market.fetchMarketItems()
    items = await Promise.all(items.map(async i => {
      const tokenUri = await nft.tokenURI(i.tokenId)
      let item = {
        price: i.price.toString(),
        tokenId: i.tokenId.toString(),
        seller: i.seller,
        owner: i.owner,
        tokenUri
      }
      return item
    }))
    console.log('items: ', items)
  })
})
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To run the test, run npx hardhat test from your command line:

Running the test

If the test runs successfully, it should log out an array containing a single marketplace item.

Building the front end

Now that the smart contract is working and ready to go, we can start building out the UI.

The first thing we might think about is setting up a layout so that we can enable some navigation that will persist across all pages.

To set this up, open pages/_app.js and update it with the following code:

View the gist here

/* pages/_app.js */
import '../styles/globals.css'
import Link from 'next/link'

function MyApp({ Component, pageProps }) {
  return (
    <div>
      <nav className="border-b p-6">
        <p className="text-4xl font-bold">Metaverse Marketplace</p>
        <div className="flex mt-4">
          <Link href="/">
            <a className="mr-4 text-pink-500">
              Home
            </a>
          </Link>
          <Link href="/create-item">
            <a className="mr-6 text-pink-500">
              Sell Digital Asset
            </a>
          </Link>
          <Link href="/my-assets">
            <a className="mr-6 text-pink-500">
              My Digital Assets
            </a>
          </Link>
          <Link href="/creator-dashboard">
            <a className="mr-6 text-pink-500">
              Creator Dashboard
            </a>
          </Link>
        </div>
      </nav>
      <Component {...pageProps} />
    </div>
  )
}

export default MyApp
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The navigation has links for the home route as well as a page to sell a digital asset, view the assets you have purchased, and a creator dashboard to see the assets you've created as well as the assets you've sold.

Querying the contract for marketplace items

The next page we'll update is pages/index.js. This is the main entry-point of the app, and will be the view where we query for the digital assets for sale and render them to the screen.

View the gist here

/* pages/index.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from "web3modal"

import {
  nftaddress, nftmarketaddress
} from '../config'

import NFT from '../artifacts/contracts/NFT.sol/NFT.json'
import Market from '../artifacts/contracts/Market.sol/NFTMarket.json'

export default function Home() {
  const [nfts, setNfts] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    /* create a generic provider and query for unsold market items */
    const provider = new ethers.providers.JsonRpcProvider()
    const tokenContract = new ethers.Contract(nftaddress, NFT.abi, provider)
    const marketContract = new ethers.Contract(nftmarketaddress, Market.abi, provider)
    const data = await marketContract.fetchMarketItems()

    /*
    *  map over items returned from smart contract and format 
    *  them as well as fetch their token metadata
    */
    const items = await Promise.all(data.map(async i => {
      const tokenUri = await tokenContract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenUri)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        image: meta.data.image,
        name: meta.data.name,
        description: meta.data.description,
      }
      return item
    }))
    setNfts(items)
    setLoadingState('loaded') 
  }
  async function buyNft(nft) {
    /* needs the user to sign the transaction, so will use Web3Provider and sign it */
    const web3Modal = new Web3Modal()
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()
    const contract = new ethers.Contract(nftmarketaddress, Market.abi, signer)

    /* user will be prompted to pay the asking proces to complete the transaction */
    const price = ethers.utils.parseUnits(nft.price.toString(), 'ether')   
    const transaction = await contract.createMarketSale(nftaddress, nft.tokenId, {
      value: price
    })
    await transaction.wait()
    loadNFTs()
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="px-20 py-10 text-3xl">No items in marketplace</h1>)
  return (
    <div className="flex justify-center">
      <div className="px-4" style={{ maxWidth: '1600px' }}>
        <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} />
                <div className="p-4">
                  <p style={{ height: '64px' }} className="text-2xl font-semibold">{nft.name}</p>
                  <div style={{ height: '70px', overflow: 'hidden' }}>
                    <p className="text-gray-400">{nft.description}</p>
                  </div>
                </div>
                <div className="p-4 bg-black">
                  <p className="text-2xl mb-4 font-bold text-white">{nft.price} ETH</p>
                  <button className="w-full bg-pink-500 text-white font-bold py-2 px-12 rounded" onClick={() => buyNft(nft)}>Buy</button>
                </div>
              </div>
            ))
          }
        </div>
      </div>
    </div>
  )
}
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When the page loads, we query the smart contract for any items that are still for sale and render them to the screen along with metadata about the items and a button for purchasing them.

Creating and listing digital items

Next, let's create the page that allows users to create and list digital assets.

There are a few things happening in this page:

  1. The user is able to upload and save files to IPFS
  2. The user is able to create a new unique digital item (NFT)
  3. The user is able to set metadata and price of item and list it for sale on the marketplace

After the user creates and lists an item, they are re-routed to the main page to view all of the items for sale.

View the gist here

/* pages/create-item.js */
import { useState } from 'react'
import { ethers } from 'ethers'
import { create as ipfsHttpClient } from 'ipfs-http-client'
import { useRouter } from 'next/router'
import Web3Modal from 'web3modal'

const client = ipfsHttpClient('https://ipfs.infura.io:5001/api/v0')

import {
  nftaddress, nftmarketaddress
} from '../config'

import NFT from '../artifacts/contracts/NFT.sol/NFT.json'
import Market from '../artifacts/contracts/Market.sol/NFTMarket.json'

export default function CreateItem() {
  const [fileUrl, setFileUrl] = useState(null)
  const [formInput, updateFormInput] = useState({ price: '', name: '', description: '' })
  const router = useRouter()

  async function onChange(e) {
    const file = e.target.files[0]
    try {
      const added = await client.add(
        file,
        {
          progress: (prog) => console.log(`received: ${prog}`)
        }
      )
      const url = `https://ipfs.infura.io/ipfs/${added.path}`
      setFileUrl(url)
    } catch (error) {
      console.log('Error uploading file: ', error)
    }  
  }
  async function createMarket() {
    const { name, description, price } = formInput
    if (!name || !description || !price || !fileUrl) return
    /* first, upload to IPFS */
    const data = JSON.stringify({
      name, description, image: fileUrl
    })
    try {
      const added = await client.add(data)
      const url = `https://ipfs.infura.io/ipfs/${added.path}`
      /* after file is uploaded to IPFS, pass the URL to save it on Polygon */
      createSale(url)
    } catch (error) {
      console.log('Error uploading file: ', error)
    }  
  }

  async function createSale(url) {
    const web3Modal = new Web3Modal()
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)    
    const signer = provider.getSigner()

    /* next, create the item */
    let contract = new ethers.Contract(nftaddress, NFT.abi, signer)
    let transaction = await contract.createToken(url)
    let tx = await transaction.wait()
    let event = tx.events[0]
    let value = event.args[2]
    let tokenId = value.toNumber()
    const price = ethers.utils.parseUnits(formInput.price, 'ether')

    /* then list the item for sale on the marketplace */
    contract = new ethers.Contract(nftmarketaddress, Market.abi, signer)
    let listingPrice = await contract.getListingPrice()
    listingPrice = listingPrice.toString()

    transaction = await contract.createMarketItem(nftaddress, tokenId, price, { value: listingPrice })
    await transaction.wait()
    router.push('/')
  }

  return (
    <div className="flex justify-center">
      <div className="w-1/2 flex flex-col pb-12">
        <input 
          placeholder="Asset Name"
          className="mt-8 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, name: e.target.value })}
        />
        <textarea
          placeholder="Asset Description"
          className="mt-2 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, description: e.target.value })}
        />
        <input
          placeholder="Asset Price in Eth"
          className="mt-2 border rounded p-4"
          onChange={e => updateFormInput({ ...formInput, price: e.target.value })}
        />
        <input
          type="file"
          name="Asset"
          className="my-4"
          onChange={onChange}
        />
        {
          fileUrl && (
            <img className="rounded mt-4" width="350" src={fileUrl} />
          )
        }
        <button onClick={createMarket} className="font-bold mt-4 bg-pink-500 text-white rounded p-4 shadow-lg">
          Create Digital Asset
        </button>
      </div>
    </div>
  )
}
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Viewing only the items purchased by the user

In the Market.sol smart contract, we created a function named fetchMyNFTs that only returns the items owned by the user.

In pages/my-assets.js, we will use that function to fetch and render them.

This functionality is different than the query main pages/index.js page because we need to ask the user for their address and use it in the contract, so the user will have to sign the transaction for it to be able to fetch them properly.

View the gist here

/* pages/my-assets.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from "web3modal"

import {
  nftmarketaddress, nftaddress
} from '../config'

import Market from '../artifacts/contracts/Market.sol/NFTMarket.json'
import NFT from '../artifacts/contracts/NFT.sol/NFT.json'

export default function MyAssets() {
  const [nfts, setNfts] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    const web3Modal = new Web3Modal({
      network: "mainnet",
      cacheProvider: true,
    })
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    const marketContract = new ethers.Contract(nftmarketaddress, Market.abi, signer)
    const tokenContract = new ethers.Contract(nftaddress, NFT.abi, provider)
    const data = await marketContract.fetchMyNFTs()

    const items = await Promise.all(data.map(async i => {
      const tokenUri = await tokenContract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenUri)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        image: meta.data.image,
      }
      return item
    }))
    setNfts(items)
    setLoadingState('loaded') 
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="py-10 px-20 text-3xl">No assets owned</h1>)
  return (
    <div className="flex justify-center">
      <div className="p-4">
        <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} className="rounded" />
                <div className="p-4 bg-black">
                  <p className="text-2xl font-bold text-white">Price - {nft.price} Eth</p>
                </div>
              </div>
            ))
          }
        </div>
      </div>
    </div>
  )
}
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Creator dashboard

The final page we will be creating is the creator dashboard that will allow them to view both all of the items they have created as well as the items they have sold.

This page will be using the fetchItemsCreated function from the Market.sol smart contract which returns only the items that match the address of the user making the function call.

On the client, we use the sold boolean to filter the items into another separate array to show the user only the items that have been sold.

Create a new file called creator-dashboard.js in the pages directory with the following code:

View the gist here

/* pages/creator-dashboard.js */
import { ethers } from 'ethers'
import { useEffect, useState } from 'react'
import axios from 'axios'
import Web3Modal from "web3modal"

import {
  nftmarketaddress, nftaddress
} from '../config'

import Market from '../artifacts/contracts/Market.sol/NFTMarket.json'
import NFT from '../artifacts/contracts/NFT.sol/NFT.json'

export default function CreatorDashboard() {
  const [nfts, setNfts] = useState([])
  const [sold, setSold] = useState([])
  const [loadingState, setLoadingState] = useState('not-loaded')
  useEffect(() => {
    loadNFTs()
  }, [])
  async function loadNFTs() {
    const web3Modal = new Web3Modal({
      network: "mainnet",
      cacheProvider: true,
    })
    const connection = await web3Modal.connect()
    const provider = new ethers.providers.Web3Provider(connection)
    const signer = provider.getSigner()

    const marketContract = new ethers.Contract(nftmarketaddress, Market.abi, signer)
    const tokenContract = new ethers.Contract(nftaddress, NFT.abi, provider)
    const data = await marketContract.fetchItemsCreated()

    const items = await Promise.all(data.map(async i => {
      const tokenUri = await tokenContract.tokenURI(i.tokenId)
      const meta = await axios.get(tokenUri)
      let price = ethers.utils.formatUnits(i.price.toString(), 'ether')
      let item = {
        price,
        tokenId: i.tokenId.toNumber(),
        seller: i.seller,
        owner: i.owner,
        sold: i.sold,
        image: meta.data.image,
      }
      return item
    }))
    /* create a filtered array of items that have been sold */
    const soldItems = items.filter(i => i.sold)
    setSold(soldItems)
    setNfts(items)
    setLoadingState('loaded') 
  }
  if (loadingState === 'loaded' && !nfts.length) return (<h1 className="py-10 px-20 text-3xl">No assets created</h1>)
  return (
    <div>
      <div className="p-4">
        <h2 className="text-2xl py-2">Items Created</h2>
          <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
          {
            nfts.map((nft, i) => (
              <div key={i} className="border shadow rounded-xl overflow-hidden">
                <img src={nft.image} className="rounded" />
                <div className="p-4 bg-black">
                  <p className="text-2xl font-bold text-white">Price - {nft.price} Eth</p>
                </div>
              </div>
            ))
          }
        </div>
      </div>
        <div className="px-4">
        {
          Boolean(sold.length) && (
            <div>
              <h2 className="text-2xl py-2">Items sold</h2>
              <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-4 gap-4 pt-4">
                {
                  sold.map((nft, i) => (
                    <div key={i} className="border shadow rounded-xl overflow-hidden">
                      <img src={nft.image} className="rounded" />
                      <div className="p-4 bg-black">
                        <p className="text-2xl font-bold text-white">Price - {nft.price} Eth</p>
                      </div>
                    </div>
                  ))
                }
              </div>
            </div>
          )
        }
        </div>
    </div>
  )
}
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Running the project

To run the project, we will need to have a deploy script to deploy the smart contracts to the blockchain network.

Deploying the contracts to a local network

When we created the project, Hardhat created an example deployment script at scripts/sample-script.js.

To make the purpose of this script more clear, update the name of scripts/sample-script.js to scripts/deploy.js.

Next, update the main function in scripts/deploy.js with the following code:

async function main() {
  const NFTMarket = await hre.ethers.getContractFactory("NFTMarket");
  const nftMarket = await NFTMarket.deploy();
  await nftMarket.deployed();
  console.log("nftMarket deployed to:", nftMarket.address);

  const NFT = await hre.ethers.getContractFactory("NFT");
  const nft = await NFT.deploy(nftMarket.address);
  await nft.deployed();
  console.log("nft deployed to:", nft.address);
}
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This script will deploy both contracts to the blockchain network.

We will first test this on a local network, then deploy it to the Mumbai testnet.

To spin up a local network, open your terminal and run the following command:

npx hardhat node
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This should create a local network with 19 accounts.

Hardhat node

Next, keep the node running and open a separate terminal window to deploy the contract.

In a separate window, run the following command:

npx hardhat run scripts/deploy.js --network localhost
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When the deployment is complete, the CLI should print out the addresses of the contracts that were deployed:

Contract addresses

Using these addresses, create a new file at the root of the project named config.js and add the following code, replacing the placeholder with the contract addresses printed out by the CLI:

export const nftmarketaddress = "nft-contract-address"
export const nftaddress = "market-contract-address"
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Importing accounts into MetaMask

You can import the accounts created by the node into your Metamask wallet to try out in the app.

Each of these accounts is seeded with 10000 ETH.

To import one of these accounts, first switch your MetaMask wallet network to Localhost 8545.

Localhost Network

Next, in MetaMask click on Import Account from the accounts menu:

MetaMask import account

Copy then paste one of the Private Keys logged out by the CLI and click Import. Once the account is imported, you should see some the Eth in the account:

MetaMask account

I'd suggest doing this with 2 or 3 accounts so that you have the ability to test out the various functionality between users.

Running the app

Now we can test out the app!

To start the app, run the following command in your CLI:

npm run dev
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To test everything out, try listing an item for sale, then switching to another account and purchasing it.

Deploying to Polygon

Now that we have the project up and running and tested locally, let's deploy to Polygon. We'll start by deploying to Mumbai, the Matic test network.

The first thing we will need to do is save one of our private keys from our wallet to the .secrets file.

To get the private key, you can use one of the private keys given to you by Hardhat or you can export them directly from MetaMask.

Private keys

For production apps, I'd suggest never hardcoding private key values in your as we are doing here, but instead setting it as something like an environment variable.

Configuring the network

Next, we need to switch from the local test network to the Mumbai Testnet.

To do so, we need to create and set the network configuration.

First, open MetaMask and click on Settings.

MetaMask settings

Next, click on Networks and then Add Network:

New Network

Here, we will add the following configurations for the Mumbai test network as listed here:

Network Name: Mumbai TestNet
New RPC URL: https://rpc-mumbai.matic.today
Chain ID: 80001
Currency Symbol: Matic

Save this, then you should be able to switch to and use the new network!

Finally, you will need some testnet Matic tokens in order to interact with the applications.

To get these, you can visit the Matic Faucet, inputting the address of the wallets that you would like to request the tokens.

Deploying to the Matic / Polygon network

Now that you have some Matic tokens, you can deploy to the Polygon network!

To do so, be sure that the address associated with the private key you are deploying your contract with has received some Matic tokens in order to pay the gas fees for the transaction.

To deploy to Matic, run the following command:

npx hardhat run scripts/deploy.js --network mumbai
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Once the contracts have been deployed, you should be able to update the contract addresses in your project and test on the new network 🎉!

npm run dev
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Deploying to Mainnet

To deploy to the main Matic / Polygon network, you can use the same steps we set up for the Mumbai test network.

The main difference is that you'll need to use an endpoint for Matic as well as import the network into your MetaMask wallet as listed here.

An example update in your project to make this happen might look like this:

/* hardhat.config.js */

/* adding Matic main network config to existing config */
...
matic: {
  url: "https://rpc-mainnet.maticvigil.com",
  accounts: [privateKey]
}
...
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Public RPCs like the one listed above may have traffic or rate-limits depending on usage. You can sign up for a dedicated free RPC URL using services like Infura, MaticVigil, QuickNode, Chainstack, or Ankr.

For example, using something like Infura:

url: `https://polygon-mainnet.infura.io/v3/${infuraId}`
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To view the final source code for this project, visit this repo

Next steps

Congratulations! You've deployed a non-trivial app to Polygon.

The coolest thing about working with solutions like Polygon is how little extra work or learning I had to do compared to building directly on Ethereum. Almost all of the APIs and tooling in these layer 2's and sidechains remain the same, making any skills transferable across various platforms like Polygon.

For the next steps, I'd suggest porting over the queries implemented in this app using The Graph. The Graph will open up many more data access patterns including things like pagination, filtering, and sorting which are necessary for any real-world application.

I will also be publishing a tutorial showing how to use Polygon with The Graph in the coming weeks.

Discussion (36)

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btandayamo profile image
Bertil Tandayamo • Edited

I had same issue with JsonRpcProvider, so I did

//index.js
const provider = new ethers.providers.JsonRpcProvider('https://rpc-mainnet.maticvigil.com')
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Deploy again on mumbai test net, copy new contract address to config file and voila
PSD. Remember to have same url in metamask wallet, hardhat config file and index.js

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giuseppecrj profile image
G.

Amazing article as always @dabit3

One small error I found is on sample-test.js instead of:

        tokenId: i.price.toString(),
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it should be

        tokenId: i.tokenId.toString(),
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dabit3 profile image
Nader Dabit Author

Thank you! And thanks for the heads up, fixing this now!

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sumeetchawla profile image
Sumeet Chawla

Hey Nader! This is such a brilliant article and a youtube video. I tried my hands at it and am falling in love with Blockchain.

So, if I am understanding it right, the listing fees should reflect in the owner's account when a certain sale happens right? But I am unable to see it. I will try to revisit the code and figure out why it isn't happening.

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dabit3 profile image
Nader Dabit Author

Amazing to hear! Yes! This should be the case. Maybe consider bumping the listing fee up high to see it show up, maybe something like equivalent of 100 or 1000 Matic

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sumeetchawla profile image
Sumeet Chawla

Thank you so much for replying. Yes, I did try it with 1000 matic. But it was still not working. It was a very stupid mistake from my end. Out of the three accounts on metamask, one was actually not imported using the keys generated in the hardhat node command 😅 I used that account's private key to initialise the market contract lol.

I was tearing my hair in trying to figure out why it wasn't working as the code made perfect sense.

Great work though. Looking forward to the next article. :D How to create a yield farm 🙈

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emmanuelmartinez profile image
Emaxnuel

Hello everyone :)

I have this error in my-assets.js:

Unhandled Runtime Error

Error: call revert exception (method="fetchMyNFTs()", errorSignature=null, errorArgs=[null], reason=null, code=CALL_EXCEPTION, version=abi/5.0.0-beta.156)

I copied and pasted the code from Github, I already looked everywhere on the Web but I can't figure it out because I don't fully understand what it is

I feel so desperate and frustrated, so useless :(

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sumeetchawla profile image
Sumeet Chawla • Edited

You are calling the JsonRpcProvider but initialising it with a public rpc url while running a local node. Remove that and it should work fine. 👍🏼

const provider = new ethers.providers.JsonRpcProvider() in index page

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btandayamo profile image
Bertil Tandayamo
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ayumirage profile image
Ayumirage • Edited

im stuck on this error:

./pages/index.js:10:0
Module not found: Can't resolve '../artifacts/contracts/Market.sol/NFTMarket.json'
8 |
9 | import NFT from "../artifacts/contracts/NFT.sol/NFT.json";

10 | import Market from "../artifacts/contracts/Market.sol/NFTMarket.json";
11 |
12 | export default function Home() {
13 | const [nfts, setNfts] = useState([]);

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sumeetchawla profile image
Sumeet Chawla

If you are running on local, you haven't compiled or tested your code and hence the artifacts are not generated.

If you are trying to build on vercel, this will come cause again the artifacts are missing. The general practice is not to commit those. Add a compile (or test) command to your build script before building nextjs.

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btandayamo profile image
Bertil Tandayamo

Please elaborate

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zhaluza profile image
Zac Haluza

I'm getting the following error when I enter pragma solidity ^0.8.3 at the top of my smart contracts:

Source file requires different compiler version (current compiler is 0.7.3+commit.9bfce1f6.Emscripten.clang) - note that nightly builds are considered to be strictly less than the released version
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Even after reinstalling my dependencies, my yarn.lock file still lists solc "0.7.3" as a dependency of hardhat@^2.5.0. Right now I'm using 0.7.3 as the Solidity version of my smart contracts - doubt it'll cause any issues for a smaller project like this, but I'm curious about how to get around it, or if that's even necessary.

Looking forward to finishing this project! Wrapping my head about how to build apps in the Web 3.0 paradigm has been both challenging and exciting, and I appreciate you putting such a huge effort into creating this type of much-needed content.

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nezzrx profile image
Nezzar Kefif

Amazing ! Juste went though it today. Now if we were to use Polygon, the contracts would need to handle both tokens right ? Because having the prices in ETH on Polygon would not work right ? Or I guess the entire market place would need to be on Polygon. Either way amazing work !

PS: I had some trouble with the JsonRpcProvider function which would still return localhost. Make sure you update .secret BEFORE deploying the Smart Contracts to the Mumbai testnet. (Already stated in the article, but I tend to read diagonally... )

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hoangsonsky profile image
hoangsonsky

Thanks. I try to deploy to the ropsten network but I have a mistake.
It is Error: call revert exception (method="fetchMarketItems()", errorArgs=null, errorName=null, errorSignature=null, reason=null, code=CALL_EXCEPTION, version=abi/5.4.0)
How can I fix it?

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lpatipat profile image
lpatipat

Getting a json rpc error on the creator-dashboard after deploying to mumbai. Worked perfectly in localhost though. Do I need to change the arguments to web3modal there too?

It looks like this

inpage.js:1 MetaMask - RPC Error: Internal JSON-RPC error.
{code: -32603, message: "Internal JSON-RPC error.", data: {…}}
code: -32603
data: {code: 3, data: "0x08c379a00000000000000000000000000000000000000000…4656e7420746f6b656e000000000000000000000000000000", message: "execution reverted: ERC721URIStorage: URI query for nonexistent token"}
message: "Internal JSON-RPC error."

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frankismartinez profile image
frank martinez

Superb walkthrough Nader, gracias!

Had to change import web3 from 'web3' to import web3 from 'web3-utils' in create-item.js

Otherwise very easy to get it up/running.

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dabit3 profile image
Nader Dabit Author

Hey, thanks, I actually meant to remove web completely and just use ethers, just updated to do so!

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jamesonhill profile image
Jameson Hill

This is awesome, thanks @dabit3 ! Question. In the deploy script, what's the difference between deploying the NFTMarket contract and NFT contract? The former calls deploy() with no args, whereas the later calls deploy(NFTMarket.address).

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sumeetchawla profile image
Sumeet Chawla

If you look at the constructor for NFT smart contract, it requires the NFTMarket address.

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frankismartinez profile image
frank martinez

Superb walkthrough Nader, gracias!

Had to change import web3 from 'web3' to import web3 from 'web3-utils' in create-item.js

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rich1n profile image
Richard Rodrigues

Hey @dabit3 nice article but the NFT.sol is a JavaScript code (the same as pages/index.js)

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rich1n profile image
Richard Rodrigues

here's the code for NFT.sol

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dabit3 profile image
Nader Dabit Author

Hey, do you mind double checking that, it looks fine to me. I have noticed that Dev.to sometimes renders gist incorrectly, so wondering if you ran into that bug.

Thread Thread
dabit3 profile image
Nader Dabit Author

Just confirmed the bug: loom.com/share/c8d473bef6224087ac8...

Try refreshing the page. Reporting this now.

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thejuju profile image
Julien Gabriel

This is crazy. Wonderful post @dabit3 !

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frankismartinez profile image
frank martinez

Superb walkthrough Nader, gracias!

Had to change import web3 from 'web3' to import web3 from 'web3-utils' in create-item.js

Otherwise very easy to get it up/running.

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meekaphro profile image
Quentin

learned so much, thanks for this

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genie_anabelle profile image
Genie Anabelle • Edited

Hi, I'm having a runtime error in create-item.js when clicking to create the listing! Would appreciate any help, thank you!

The error is regarding: let value = event.args[2]

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baart1989 profile image
baart1989 • Edited

I had similar in my case it was that i had to re-run deploy.js command.

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mosesibe profile image
moze

Thank you for this

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lgs profile image
Luca G. Soave • Edited

Super !!!

For the future, why not SvelteKit instead of Next.js ?

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dabit3 profile image
Nader Dabit Author

No huge reason really other than that I am already really experienced with Next.js. Will try using SvelteKit next time :)

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marc_nahas profile image
Marc Nahas

Hi Nader,
This content is amazing but I keep having the following error and I don't get how to fix it.
Thank you forward for your help :)
Have a good day !

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vorcigernix profile image
Adam Sobotka

Nice article, thanks. I am getting
reason: 'could not detect network',
code: 'NETWORK_ERROR',
event: 'noNetwork',
when I try to deploy to mumbai. Any idea what could be wrong?

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vorcigernix profile image
Adam Sobotka • Edited

Also getting a weird metamask RPC errors, like
message: "NetworkError when attempting to fetch resource." or similar with empty message. I found some related reports, could be caused by some metamask/firefox combination. Weird is that it works fine on localhost. Could be some Matic issue? Also tried to switch to infura RPC, didn't help. Any idea what can I try?