Implementing an Oracle

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Challenge 4 - Implementing an Oracle 🔮
Getting Started
git clone https://github.com/scaffold-eth/scaffold-eth-challenges.git app
cd app
git checkout challenge-4-oracle
yarn install
How Do Smart Contracts Use Oracles?
Oracles are most popularly used with Data Feeds. DeFi platforms like AAVE and Synthetix use Chainlink data feed oracles to obtain accurate real-time asset prices in their smart contracts.
Chainlink data feeds are sources of data aggregated from many independent Chainlink node operators. Each data feed has an on-chain address and functions that enable contracts to read from that address. For example, the ETH / USD feed.
An Aggregator Page for ETH / USD
Using Chainlink Data Feeds
The following code is from the Get the Latest Price page. It describes a contract which obtains the latest ETH / USD price using the Kovan testnet.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
​
import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";
​
contract PriceConsumerV3 {
​
    AggregatorV3Interface internal priceFeed;
​
    /**
     * Network: Kovan
     * Aggregator: ETH/USD
     * Address: 0x9326BFA02ADD2366b30bacB125260Af641031331
     */
    constructor() {
        priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
    }
​
    /**
     * Returns the latest price
     */
    function getLatestPrice() public view returns (int) {
        (
            uint80 roundID, 
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = priceFeed.latestRoundData();
        return price;
    }
}
Notice how the code imports an interface called AggregatorV3Interface. In this case, AggregatorV3Interface defines that all V3 Aggregators will have the function latestRoundData. You can see all of the functions that a V3 Aggregator exposes in theAggregatorV3Interface file on Github.
Our contract is initialized with the hard-coded address of the Kovan data feed for ETH / USD prices. Then, getLatestPrice uses latestRoundData to obtain the most recent round of price data. We're interested in the price, so the function returns that.
 How To Deploy To Testnet
There are a few things that are needed to deploy a contract to a testnet:
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Challenge 4 - Implementing an Oracle 🔮

Getting Started

How Do Smart Contracts Use Oracles?

Using Chainlink Data Feeds

How To Deploy To Testnet