A Step-by-Step Guide to Building and Deploying a Voting Smart Contract on the Blockchain

This article was originally published at Building a Decentralized nft Marketplace

In this tutorial, we will guide you through the process of developing a voting smart contract using the Solidity programming language. We will then deploy the contract on a blockchain network and test it to ensure its functionality. By the end of this tutorial, you will have a good understanding of how to create and deploy a smart contract for voting purposes.

Step 1: Cloning the Tutorial Repo

1.1 Forking the Tutorial Repository:

• Head over to our Tutorial Repository and click on the “Fork” button to create a copy of the repository on your own account. Wait for the forking process to finish before proceeding.

1.2 Cloning the repository locally:

• Go to your forked repository on GitHub.
• Click the “Code” button and copy the HTTPS or SSH URL.
• Open your terminal or Git Bash.
• Navigate to the directory where you want to clone the repository.
• Run the below command to clone the Repo.

git clone <paste the URL you copied>

• Wait for the cloning process to complete. Once it’s done, you should see a new directory with the name of the repository in the directory.
• To move into the cloned repository, use this commandcd <Name of the cloned Repo> , then move to the voting folder use this commandcd Voting .

Step 2: Developing Election Smart Contract

Below is the code for our smart contract. You can get it from here Election. sol.

Let’s run through our smart contract real quick 🏃

• Basic details about the election — This block of code would be storing basic details of each Election contract. Details include name and description.

• Storing candidate details — Candidate details would be stored in a mapping between an unsigned integer to the Candidate structure. Candidate the structure would consist of data like id, name (candidate's name), and voteCount (number of times they are voted).

• Storing details of voters who have already voted and the number of candidates — voters is a mapping between the address of the voter and a boolean. In Solidity, the default boolean value is false, so if the returned value of voters(address) is false we can understand that the voters are voting for the first time in this election, and vice-versa for true.

• Constructor call and adding candidates to the election — When a smart contract is deployed on a network, the first thing to be called is a constructor() function. Whatever we want to initialize in a smart contract, we do it inside the constructor() function. Like here, we will be adding a name, description, and candidates to the election. Here, addCandidate() is a private function, so that, it cannot be called publicly. This function takes name and description as a single array named _nda in the first argument and candidates' names as an array in the second argument.

• Voting candidates in an election — We made a vote() function. It takes candidateId as an argument and increments the vote of the respective candidate. It requires two things, viz. voters should not have voted in the particular election by checking the boolean across the voters mapping and candidateId should be a valid one, i.e. 0 <= candidateId < candiatesCount.

MainContract.sol

MainContract.sol is the main entry point of our e-voting DApp. It will maintain the number of election contracts deployed, and their address on the network and will also help in deploying them. We have also imported Election.sol a contract, for using it in the MainContract.sol.

• Here electionId is used for assigning IDs to each election that a user creates and is incremented for using it while creating the next election. Also, Elections is a public mapping between electionId and the address of the deployed election contract.

• We have made a createElection() the function which will be used to deploy our Election smart contract. This function takes name and description as a single array named _nda in the first argument and candidates’ names as an array in the second argument.

Here you can see that a new Election contract is deployed on the network using the new keyword. And the address for the deployed smart contract is stored in the Elections mapping. Once the election contract is deployed successfully, electionId is incremented.

Step 3: Getting up the infra needed to deploy and test our smart contract

3.1. Visit the BuildBear App (why BuildBear: Read article here).

3.2. Create your Private Testnet forking from the Ethereum Mainnet, feel free to fork any Chain.

3.3. Add your Private Testnet to your MetaMask wallet by using the “Add to Metamask” button:

3.4. Click on Open Faucet you will be redirected to Faucet Pages, and then Mint native Tokens to pay for gas for the transactions.

Step 4: Deploying the Smart Contract

For installing the necessary packages, please execute the following command: npm install .

4.1 Update thehardhat.config.js .

• Head to your Dashboard and click on “verify contract”.

• Copy the BuildBear and Etherscan objects, and update the hardhat.config.js file.
• To deploy the maincontract.sol the smart contract runs the deploy command. This will run the deployment script in deploy/00_deploy_mainContract.jsand save the deployment details along with ABI and Contract address.

npx hardhat deploy

Click on the link provided in the terminal to see the Contract on Explore page.

WOOT WOOT 🎉 🎉

4.2. Creating an Election

The scripts for invoking the createElection function and verifying the Election contract have already been configured in the scripts/deployElectionContract.js file, as demonstrated above. To execute the scripts, please run the following command.

npx hardhat run scripts/deployElectionContract.js

Our new election has been successfully deployed, and the contract has been verified. To view the contract on Explore, simply click on the link provided in the terminal. This will take you directly to the Contract page, where we can read and write directly from the contract.

4.3 Casting our Vote

Enter the candidate id to see the there name and Total votes cast to them.

Let’s move to the write the contract section and cast our vote.

Now if we go back to the read and check the total votes received by Candidate 1 it will be increased by 1.

We have successfully built an Election smart contract, deployed it, created an election, and cast our vote !!! 🎉🎉🎉

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About BuildBear:

BuildBear is a platform for testing dApps at scale, for teams. It provides users with their own private Testnet to test their smart contracts and dApps, which can be forked from any EVM chain. It also provides a Faucet, Explorer, and RPC for testing purposes.

BuildBear aims to build an ecosystem of tools for testing dApps at scale for the teams.

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Authors: Chandan, Dipesh