Hello World Contract

Description: This is the simplest contract to get you started. It introduces the basic structure of a smart contract and shows how to deploy and interact with it.

Purpose: To familiarize you with the basic syntax and deployment process of smart contracts on aelf blockchain.

Difficulty Level: Easy

Step 1 - Setting up your development environment#

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dotnet new --install AElf.ContractTemplates

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dotnet tool install --global aelf.deploy

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sudo npm i -g aelf-command

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npm i -g aelf-command

Step 2 - Develop Smart Contract#

Start Your Smart Contract Project#

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mkdir hello-world
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cd hello-world
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dotnet new aelf -n HelloWorld

Adding Your Smart Contract Code#

Now that we have a template hello world project, we can customise the template to incorporate our own contract logic. Lets start by implementing methods to provide basic functionality for updating and reading a message stored persistently in the contract state.

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cd src

The implementation of file src/HelloWorldState.cs is as follows:

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using AElf.Sdk.CSharp.State;
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namespace AElf.Contracts.HelloWorld
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{
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    // The state class is access the blockchain state
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    public class HelloWorldState : ContractState
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    {
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        // A state that holds string value
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        public StringState Message { get; set; }
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    }
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}

The implementation of file src/HelloWorld.cs is as follows:

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// contract implementation starts here
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namespace AElf.Contracts.HelloWorld
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{
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    public class HelloWorld : HelloWorldContainer.HelloWorldBase
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    {
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        // A method that updates the contract state, Message with a user input
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        public override Empty Update(StringValue input)
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        {
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            State.Message.Value = input.Value;
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            Context.Fire(new UpdatedMessage
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            {
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                Value = input.Value
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            });
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            return new Empty();
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        }
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        // A method that reads the contract state, Message
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        public override StringValue Read(Empty input)
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        {
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            var value = State.Message.Value;
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            return new StringValue
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            {
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                Value = value
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            };
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        }
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    }
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}

Building Smart Contract#

Build the new code with the following commands inside src folder:

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dotnet build

Step 3 - Deploy Smart Contract#

Create A Wallet#

To send transactions on the aelf blockchain, you must have a wallet.

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aelf-command create

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? Save account info into a file? (Y/n) Y

Make sure to choose Y to save your account information.

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export WALLET_PASSWORD="YOUR_WALLET_PASSWORD"

Acquire Testnet Tokens (Faucet) for Development#

To deploy smart contracts or execute on-chain transactions on aelf, you'll require testnet ELF tokens.

Get ELF Tokens

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export WALLET_ADDRESS="YOUR_WALLET_ADDRESS"
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curl -X POST "https://faucet.aelf.dev/api/claim?walletAddress=$WALLET_ADDRESS" -H "accept: application/json" -d ""

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aelf-command call ASh2Wt7nSEmYqnGxPPzp4pnVDU4uhj1XW9Se5VeZcX2UDdyjx -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io GetBalance

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Enter the required param <symbol>: ELF
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Enter the required param <owner>: $WALLET_ADDRESS

Deploy Smart Contract:

The smart contract needs to be deployed on the chain before users can interact with it.

Run the following command to deploy a contract. Remember to export the path of LotteryGame.dll.patched to CONTRACT_PATH.

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export CONTRACT_PATH=$(find ~+ . -path "*patched*" | head -n 1)

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aelf-deploy -a $WALLET_ADDRESS -p $WALLET_PASSWORD -c $CONTRACT_PATH -e https://tdvw-test-node.aelf.io/

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export CONTRACT_ADDRESS="YOUR_SMART_CONTRACT_ADDRESS e.g. 2LUmicHyH4RXrMjG4beDwuDsiWJESyLkgkwPdGTR8kahRzq5XS"

Step 4 - Interact with Your Deployed Smart Contract#

Lets try to call methods on your newly-deployed smart contract using aelf-command.

Firstly, we will set a message using the Update method. Run the following command, and enter the message argument as test. This will set test into the Message contract state. Remember to export CONTRACT_ADDRESS equals to your deployed contract address.

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aelf-command send $CONTRACT_ADDRESS -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Update

After that, we can use Read method to retrieve the value previously set for the Message contract state. Running the following command should yield test.

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aelf-command call $CONTRACT_ADDRESS -a $WALLET_ADDRESS -p $WALLET_PASSWORD -e https://tdvw-test-node.aelf.io Read

🎯 Conclusion#

🎊 Congratulations!#

You've successfully completed the Hello World Contract tutorial! Awesome job sticking with it until the end. 🌟

📚 What You've Learned#

In this tutorial, you've discovered:

🔍 Final Output#

By now, you should have:

To verify, you should have seen the test message returned when you called the Read method after setting it using the Update method. If you see this message, you've nailed it! 🏆

➡️ What's Next?#

Now that you've got the basics down, why not dive into more advanced topics or other tutorials like the Lottery Game Contract or Voting Contract?

Keep experimenting and building to level up your aelf blockchain development skills. 🚀

Happy coding! 😊

Edited on: 21 July 2024 06:14:21 GMT+0