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

Step 2 - Develop Smart Contract#

Start Your Smart Contract Project#

Open your Terminal.

Enter the following command to generate a new 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.

Run this command to create aelf wallet.

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aelf-command create

You will be prompted to save your account, please do save your account as shown below:

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

Next, enter and confirm your password. Then export your wallet password as shown below:

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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

Run the following command to get testnet ELF tokens from faucet. Remember to either export your wallet address and wallet password or replace your wallet address and wallet password respectively.

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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 ""

To check your wallet's current ELF balance:

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

You will be prompted for the following:

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

You should see the result displaying your wallet's ELF balance.

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/

Please wait for approximately 1 to 2 minutes. If the deployment is successful, it will provide you with the contract address.

Export your smart contract address:

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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: 15 July 2024 05:03:03 GMT+0