Introduction
We will be creating the smart contract for a charity donation platform in this post. Yes, something like Gofundme but on the blockchain.
and users can donate to individual campaigns with Ether.
Expectations
This post assumes you are already familiar with the structure of a smart contract and basic types in solidity.
Required tools
- Remix (a browser-based IDE)
- Any browser (preferably Chrome)
Overview
Our platform will allow anyone to create a charity/donation campaign and set a time limit or deadline for it, After creating the campaign, a user can donate to any campaign they choose to support and the creator of the campaign can withdraw all the funds donated to the campaign after the deadline is exceeded.
Enough talk, let's get started with the code
First, we'll create our contract file and name it Charity.sol. The we populate it with the code below;
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;
import "@openzeppelin/contracts/utils/Counters.sol";
contract Charity {
}
The first and second line in the code above defines the license and the solidity version for compiling the code. Then we import a library from openzeppelin called Counters.sol which provides us with counters that can only be incremented or decremented.
Next, we define a new contract called Charity
To give us a sense of direction, we will create all the functions skeleton we need before implementing them one by one.
contract Charity {
using Counters for Counters.Counter;
// These are events to be emitted when specific actions are completed
event CampaignStarted(bytes32 campaignId, address initiator);
event WithdrawFunds(bytes32 campaignId, address initiator, uint256 amount);
event FundsDonated(bytes32 campaignId, address donor, uint256 amount);
// defines a variable to keep track of total number of campaigns created
Counters.Counter public _campaignCount;
// Campaign details to be saved
struct Campaign {
string title;
string imgUrl;
string description;
uint256 fundsRaised;
bool isLive;
address initiator;
uint256 deadline;
uint256 balance;
}
// allows us to keep track of the campaigns created and it's details using a unique ID
mapping(bytes32=>Campaign) public _campaigns;
// allows us to keep track of the who donates to a campaign and the amount they donated
mapping(address=>mapping(bytes32=>uint256)) public userCampaignDonations;
// this function generated a unique ID for a campaign
//from it's title, descrition and creator address
function generateCampaignId(address initiator, string calldata title, string calldata description) public pure returns(bytes32) { }
// this function will be called by a user to create a new campaign
function startCampaign( string calldata title, string calldata description, string calldata imgUrl, uint256 deadline ) public { }
// calling this function allows users to donate to a charity campaign of their choice
function donateToCampaign(bytes32 campaignId) public payable { }
// returns the details of a campaign given the campaignId
function getCampaign(bytes32 campaignId) public view returns(Campaign memory) { }
// this function allows the creator of the campaign to withdraw all the funds donated to the campaign
// after the campaign has ended
function withdrawCampaignFunds(bytes32 campaignId) public { }
}
Now let's take the functions one after the other and flesh them out. First is the generateCampaignId function, this function will create a unique hash from the campaign title, description, and initiator address
function generateCampaignId(address initiator, string calldata title, string calldata description) public pure returns(bytes32) {
bytes32 campaignId = keccak256(abi.encodePacked(title, description, initiator));
return campaignId;
}
Next, we create the function startCampaign which allows a user to actually create a campaign,
function startCampaign( string calldata title, string calldata description, string calldata imgUrl, uint256 deadline ) public {
// first, we generate a campaignID
// using the title, description and the address of the initiator
bytes32 campaignId = generateCampaignId(msg.sender, title, description);
// get a reference to the campaign with the generated Id
Campaign storage campaign = _campaigns[campaignId];
// require that the campaign is not live yet.
require(!campaign.isLive, "Campaign exists");
// require the current time to be less than the campaign deadline
require(block.timestamp < deadline, "Campaign ended");
campaign.title = title;
campaign.description = description;
campaign.initiator = msg.sender;
campaign.imgUrl = imgUrl;
campaign.deadline = deadline;
campaign.isLive = true;
// increment the total number of charity campaigns created
_campaignCount.increment();
// emit an event to the blockchain
emit CampaignStarted(campaignId, msg.sender);
}
After creating the campaign, we need a way to allow users donate to a live campaign. So let's create the donateToCampaign function.
// allows users to donate to a charity campaign of their choice
function donateToCampaign(bytes32 campaignId) public payable {
// get campaign details with the given campaign
Campaign storage campaign = _campaigns[campaignId];
// end the campaign if the deadline is exceeded
if(block.timestamp > campaign.deadline){
campaign.isLive = false;
}
// require the campaign has not ended
require(block.timestamp < campaign.deadline, "Campaign has ended");
uint256 amountToDonate = msg.value;
require(amountToDonate > 0, "Wrong ETH value");
// increase the campaign balance by the amount donated;
campaign.fundsRaised += amountToDonate;
campaign.balance += amountToDonate;
// keep track of users donation history
userCampaignDonations[msg.sender][campaignId] = amountToDonate;
// emit FundsDonated event
emit FundsDonated(campaignId, msg.sender, amountToDonate);
}
Okay, users can now donate to our cause via the above function. But we still need a way for the creator of the campaign to withdraw the Ether donated to them. So let's complete the withdrawCampaignFunds function.
function withdrawCampaignFunds(bytes32 campaignId) public {
Campaign storage campaign = _campaigns[campaignId];
// require the msg.sender is the creator of the campaign
require(msg.sender == campaign.initiator, "Not campaign initiator");
// require the campaign has ended
require(!campaign.isLive, "campaign is still active");
require(block.timestamp > campaign.deadline, "Campaign is still active");
// require the campaign has funds to be withdrawn
require(campaign.balance > 0, "No funds to withdraw");
uint256 amountToWithdraw = campaign.balance;
// zero the campaign balance
campaign.balance = 0;
// transfer the balance to the initiator address;
payable(campaign.initiator).transfer(amountToWithdraw);
// emit an event to the blockchain
emit WithdrawFunds(campaignId, campaign.initiator, amountToWithdraw);
}
Cool, we now have complete flow for the donation process.
Below is the full code for this tutorial.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.6;
import "@openzeppelin/contracts/utils/Counters.sol";
contract Charity {
using Counters for Counters.Counter;
event CampaignStarted(bytes32 campaignId, address initiator);
event WithdrawFunds(bytes32 campaignId, address initiator, uint256 amount);
event FundsDonated(bytes32 campaignId, address donor, uint256 amount);
Counters.Counter public _campaignCount;
struct Campaign {
string title;
string imgUrl;
string description;
uint256 fundsRaised;
bool isLive;
address initiator;
uint256 deadline;
uint256 balance;
}
mapping(bytes32=>Campaign) public _campaigns;
mapping(address=>mapping(bytes32=>uint256)) public userCampaignDonations;
constructor(){
}
function generateCampaignId(address initiator, string calldata title, string calldata description) public pure returns(bytes32) {
bytes32 campaignId = keccak256(abi.encodePacked(title, description, initiator));
return campaignId;
}
function startCampaign( string calldata title, string calldata description, string calldata imgUrl, uint256 deadline ) public {
// generate a campaignID
// using the title, description and the address of the initiator
bytes32 campaignId = generateCampaignId(msg.sender, title, description);
// get a reference to the campaign with the generated Id
Campaign storage campaign = _campaigns[campaignId];
// require that the campaign is not live yet.
require(!campaign.isLive, "Campaign exists");
// require the current time to be less than the campaign deadline
require(block.timestamp < deadline, "Campaign ended");
campaign.title = title;
campaign.description = description;
campaign.initiator = msg.sender;
campaign.imgUrl = imgUrl;
campaign.deadline = deadline;
campaign.isLive = true;
// increment the total number of charity campaigns created
_campaignCount.increment();
// emit an event to the blockchain
emit CampaignStarted(campaignId, msg.sender);
}
function endCampaign() public {
}
// allows users to donate to a charity campaign of their choice
function donateToCampaign(bytes32 campaignId) public payable {
// get campaign details with the given campaign
Campaign storage campaign = _campaigns[campaignId];
// end the campaign if the deadline is exceeded
if(block.timestamp > campaign.deadline){
campaign.isLive = false;
}
// require the campaign has not ended
require(block.timestamp < campaign.deadline, "Campaign has ended");
uint256 amountToDonate = msg.value;
require(amountToDonate > 0, "Wrong ETH value");
// increase the campaign balance by the amount donated;
campaign.fundsRaised += amountToDonate;
campaign.balance += amountToDonate;
// keep track of users donation history
userCampaignDonations[msg.sender][campaignId] = amountToDonate;
// emit FundsDonated event
emit FundsDonated(campaignId, msg.sender, amountToDonate);
}
// returns the details of a campaign given the campaignId
function getCampaign(bytes32 campaignId) public view returns(Campaign memory) {
return _campaigns[campaignId];
}
function withdrawCampaignFunds(bytes32 campaignId) public {
Campaign storage campaign = _campaigns[campaignId];
// require the msg.sender is the creator of the campaign
require(msg.sender == campaign.initiator, "Not campaign initiator");
// require the campaign has ended
require(!campaign.isLive, "campaign is still active");
require(block.timestamp > campaign.deadline, "Campaign is still active");
// require the campaign has funds to be withdrawn
require(campaign.balance > 0, "No funds to withdraw");
uint256 amountToWithdraw = campaign.balance;
// zero the campaign balance
campaign.balance = 0;
// transfer the balance to the initiator address;
payable(campaign.initiator).transfer(amountToWithdraw);
// emit an event to the blockchain
emit WithdrawFunds(campaignId, campaign.initiator, amountToWithdraw);
}
}
Well done!!! 🎉🎉🎉
If you have been able to get here, I hope you have been able to learn more about creating smart contracts.
In the next part of this series, I'll be creating a UI for our smart contract using React or Next.js
Feel free to reach out to me on codementor If you have any suggestions or questions or if you just wanna say hi.
Top comments (3)
Thanks for sharing. i want to use this on my ehsaas programme website
Eagerly waiting for the next part of series. Can I hae a permission to use this for my nser survey online registration website.
Can i use this for my ehsaas blog?