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

Edited on: 18 July 2024 03:46:33 GMT+0