Ethereum Cookbook

How to do it...

1. Solidity does not allow you to pull data from an external API source. Use an Oracle service to achieve this functionality.
2. An oracle is an event listener that listens and responds to them by sending the results of a query back to the contract. In this way, contracts can interact with the external world.
3. As an example, assume that we have a smart contract that uses an external data service to select a random number. Let's see how we can implement it using a custom Oracle service.
4. Create a basic smart contract with a state variable to store the random number:

pragma solidity ^0.4.24;contract OracleRng {    uint public random;    ...}

5. The Oracle service listens to the event logged in the contract and then uses the log details to ...