Klaytn Docs Archive
Getting StartedBuild a dAppNode OperationDeveloper Hub
  • Klaytn Docs
  • -
    • Klaytn Overview
      • Why Klaytn
      • Klaytn Design
        • Consensus Mechanism
        • Accounts
        • Transactions
          • Basic
          • Fee Delegation
          • Partial Fee Delegation
          • Ethereum
        • Computation
          • Klaytn Smart Contract
          • Execution Model
          • Computation Cost
            • Computation Cost (Previous docs)
          • Klaytn Virtual Machine
            • Klaytn Virtual Machine (Previous docs)
        • Storage
          • State Migration
          • StateDB Live Pruning
        • Transaction Fees
          • Transaction Fees (Previous docs)
        • Klaytn native coin - KLAY
        • Token Economy
        • Governance
        • Multi-Channel
        • KNI
      • Scaling Solutions
    • Getting Started
      • Deploying Smart Contract Using Foundry
      • Deploying Smart Contract Using Hardhat
      • Deploying Smart Contract Using Thirdweb
      • Deploying Smart Contract Using KEN
        • Launch an Endpoint Node
        • Top up your Account
        • Install Development Tools
        • Deploy a Smart Contract
        • Check the Deployment
        • Account Management
          • Creating Accounts
          • Managing Accounts
      • Development Environment
      • Getting KLAY
    • Smart Contract
      • Solidity - Smart Contract Language
      • Precompiled Contracts
        • Precompiled Contracts (Previous docs)
      • IDE and Tools
        • Truffle
      • Sample Contracts
        • KlaytnGreeter
        • ERC-20
          • 1. Writing ERC-20 Smart Contract
          • 2. Deploying Smart Contract
          • 3. Interacting with ERC-20 token from Klaytn Wallet
        • ERC-721
          • 1. Writing ERC-721 Smart Contract
          • 2. Deploying Smart Contract
      • Testing Guide
      • Deployment Guide
      • Klaytn Compatible Tokens
      • Porting Ethereum Contract
    • Run a Node
      • Deployment
        • Endpoint Node
          • System Requirements
          • Installation Guide
            • Download
            • Installation Guide
            • Configuration
            • Startup the EN
            • Testing the Installation
          • ken CLI commands
          • JSON-RPC APIs
        • Core Cell
          • System Requirements
          • Network Configuration
          • Installation Guide
            • Download
            • Before You Install
            • Consensus Node Setup
              • Installation Guide
              • Configuration
              • Startup the CN
            • Proxy Node Setup
              • Installation Guide
              • Configuration
              • Startup the PN
            • Testing the Core Cell
          • Monitoring Setup
          • H/A Setup
        • Service Chain
          • Getting Started
            • Setting up a 4-node Service Chain
            • Connecting to Baobab
            • Cross-Chain Value Transfer
            • HA(High Availability) for ServiceChain
            • Nested ServiceChain
            • Value Transfer between Sibling ServiceChains
          • Reference Manuals
            • System Requirements
            • Download
            • SCN User Guide
              • Installation
              • Configuration
              • Starting/Stopping SCN
              • Checking Node Status
              • kscn commands
              • homi commands
            • SPN/SEN User Guide
              • Installation
              • Configuration
              • Starting/Stopping Node
              • Checking Node Status
            • Bridge Configuration
            • Anchoring
            • KAS Anchoring
            • Value Transfer
            • Configuration Files
            • Log Files
            • Genesis JSON
            • Upgrade & Hard Fork
          • How-To Guides
        • Download Node Packages
          • v1.12.0
          • v1.11.1
          • v1.11.0
          • v1.10.2
          • v1.10.1
          • v1.10.0
          • v1.9.1
          • v1.9.0
          • v1.8.4
          • v1.8.3
          • v1.8.2
          • v1.8.1
          • v1.8.0
          • v1.7.3
          • v1.7.2
          • v1.7.1
          • v1.7.0
          • v1.6.4
          • v1.6.3
          • v1.6.2
          • v1.6.1
          • v1.6.0
          • v1.5.3
          • v1.5.2
          • v1.5.1
          • v1.5.0
          • v1.4.2
          • v1.4.1
          • v1.4.0
          • v1.3.0
          • v1.2.0
          • v1.1.1
          • v1.0.0
          • v0.9.6
          • v0.8.2
    • Operation Guide
      • Configuration
      • Node Log
      • Log operation
      • Errors & Troubleshooting
      • Klaytn Command
      • Chaindata Change
      • Chaindata Migration
    • dApp Developers
      • JSON-RPC APIs
        • API references
          • eth
            • Caution
            • Account
            • Block
            • Transaction
            • Config
            • Filter
            • Gas
            • Miscellaneous
          • klay
            • Account
            • Block
            • Transaction
              • Working with Klaytn Transaction Types
            • Configuration
            • Filter
            • Gas
            • Miscellaneous
          • net
          • debug
            • Logging
            • Profiling
            • Runtime Tracing
            • Runtime Debugging
            • VM Tracing
            • VM Standard Tracing
            • Blockchain Inspection
          • admin
          • personal
          • txpool
          • governance
        • Service Chain API references
          • mainbridge
          • subbridge
        • Transaction Error Codes
      • RPC Service Providers
        • Public Endpoints
      • SDK & Libraries for interacting with Klaytn Node
        • caver-js
          • Getting Started
          • Sending a sample transaction
          • API references
            • caver.account
            • caver.wallet
              • caver.wallet.keyring
            • caver.transaction
              • Basic
              • Fee Delegation
              • Partial Fee Delegation
            • caver.rpc
              • caver.rpc.klay
              • caver.rpc.net
              • caver.rpc.governance
            • caver.contract
            • caver.abi
            • caver.kct
              • caver.kct.kip7
              • caver.kct.kip17
              • caver.kct.kip37
            • caver.validator
            • caver.utils
            • caver.ipfs
          • caver-js ~v1.4.1
            • Getting Started (~v1.4.1)
            • API references
              • caver.klay
                • Account
                • Block
                • Transaction
                  • Legacy
                  • Value Transfer
                  • Value Transfer Memo
                  • Account Update
                  • Smart Contract Deploy
                  • Smart Contract Execution
                  • Cancel
                • Configuration
                • Filter
                • Miscellaneous
              • caver.klay.net
              • caver.klay.accounts
              • caver.klay.Contract
              • caver.klay.KIP7
              • caver.klay.KIP17
              • caver.klay.abi
              • caver.utils (~v1.4.1)
            • Porting from web3.js
        • caver-java
          • Getting Started
          • API references
          • caver-java ~v1.4.0
            • Getting Started (~v1.4.0)
            • Porting from web3j
        • ethers.js
        • web3.js
      • Tutorials
        • Klaytn Online Toolkit
        • Fee Delegation Example
        • Count DApp
          • 1. Environment Setup
          • 2. Clone Count DApp
          • 3. Directory Structure
          • 4. Write Smart Contract
          • 5. Frontend Code Overview
            • 5-1. Blocknumber Component
            • 5-2. Auth Component
            • 5-3. Count Component
          • 6. Deploy Contract
          • 7. Run App
        • Klaystagram
          • 1. Environment Setup
          • 2. Clone Klaystagram DApp
          • 3. Directory Structure
          • 4. Write Klaystagram Smart Contract
          • 5. Deploy Contract
          • 6. Frontend Code Overview
          • 7. FeedPage
            • 7-1. Connect Contract to Frontend
            • 7-2. UploadPhoto Component
            • 7-3. Feed Component
            • 7-4. TransferOwnership Component
          • 8. Run App
        • Building a Buy Me a Coffee dApp
          • 1. Project Setup
          • 2. Creating a BMC Smart Contract
          • 3. Testing the contract using scripts
          • 4. Deploying BMC Smart contract
          • 5. Building the BMC Frontend with React and Web3Onboard
          • 6. Deploying Frontend code on IPFS using Fleek
          • 7. Conclusion
        • Migrating Ethereum App to Klaytn
        • Connecting MetaMask
        • Connecting Remix
        • Verifying Smart Contracts Using Block Explorers
      • Developer Tools
        • Wallets
          • Kaikas
          • Klaytn Wallet
          • Klaytn Safe
            • Klaytn Safe Design
            • Create a Safe
            • Add assets
            • Send assets
            • Contract Interaction
            • Transaction Builder
            • Points to Note
            • Frequently Asked Questions
          • SafePal S1
          • Wallet Libraries
            • Web3Auth
            • Web3Modal
            • Web3-Onboard
            • Particle Network
        • Oracles
          • Orakl Network
          • Witnet
          • SupraOracles
        • Indexers
          • SubQuery
        • Cross-chain
          • LayerZero
        • Block Explorers
          • Klaytnscope
          • Klaytnfinder
        • Klaytn Contracts Wizard
    • Glossary
  • ---
    • Klaytn Hard Fork History
    • Klaytn 2.0
      • Metaverse Package
      • Finality and Improvements
      • Ethereum Compatibility
      • Decentralizing Governance
      • Massive Eco Fund
    • FAQ
    • Open Source
    • Terms of Use
    • Languages
  • ℹ️Latest Klaytn Docs
Powered by GitBook
On this page
  1. -
  2. dApp Developers
  3. Tutorials
  4. Building a Buy Me a Coffee dApp

2. Creating a BMC Smart Contract

In this section we will be creating the smart contract that houses the BMC functionality. To get started, navigate to your contracts folder, create a new file named BuyMeACoffee.sol and paste this code below:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;
contract BuyMeACoffee {
    // event to emit when a message is sent with tip
    event NewCoffee(address indexed _sender, string name, string _message, uint256 _timestamp);

    // address of contract deployer
    address payable owner;
    constructor() {
        // stores deployer as owner
        owner = payable(msg.sender);
    }

    // struct of BuyMeACoffe Tx
    struct BuyCoffee {
        address sender;
        string name;
        uint timestamp;
        string message;
    }

    // maps id to BuyCoffee struct
    mapping (uint => BuyCoffee) idToBuyCoffee;

    // id 
    uint public coffeeId;

    // buy coffee function
    function buyCoffee(string memory name, string memory message) public payable {
	  // Must accept more than 0 KLAY for a coffee.
        require(msg.value > 0, "Tip must be greater than zero");
        coffeeId++;
	
	// Add the coffee tx to storage
        BuyCoffee storage coffee = idToBuyCoffee[coffeeId];
        coffee.message = message;
        coffee.name = name;
        coffee.sender = msg.sender;
        coffee.timestamp = block.timestamp;
         // Emit a NewCoffee event with details about the coffee tx.
        emit NewCoffee(msg.sender, name, message, block.timestamp);
    }

    // withdraw coffee tips to the contract owner
    function withdrawCoffeTips() public {
        require(_owner == msg.sender, "Not owner");
        require(owner.send(address(this).balance) );
    }

     // get all coffee
    function getAllCoffee(uint _id) public view returns(BuyCoffee[] memory c){
        require(_id <= coffeeId, "Non-existent id");
        c = new BuyCoffee[](_id);
        for(uint i = 0; i < _id; i++) {
            c[i] = idToBuyCoffee[i + 1];
        }
    }
}

Let's quickly go over what each line of code does:

The NewCoffee event is emitted when a buyCoffee function is executed. It logs out the address of the sender, the name of the sender, the message sent, and the timestamp.

Next is the owner variable, which represents the contract deployer. We then set the msg.sender to be the owner of the contract in our constructor.

The coffeeId was created to keep track of the coffee transaction created.

Subsequently we declared a buyMeACoffee struct, which stores all the data related to a coffee transaction; address sender, string name, uint timestamp, string message. We then mapped this struct to an id using the idToBuyCoffee variable.

The buyCoffee function is the core implementation of BMC smart contract. It is a payable function which takes in two parameters, the name and address of the sender. It checks if the KLAY amount sent in is greater than zero. Next it increments the coffeeId, then it adds the coffee tx or info to the blockchain. Finally it emits a NewCoffee event, which entails the details of the coffee tx.

We created a withdraw() function to withdraw the total balance of the contract (address(this).balance) to the owner.

Finally, a getAllCoffee() function was created. It returns all the coffee transactions created overtime.

Now that we have completed writing our BMC smart contract, the next step is to test the functionalities of our smart contract, deploy and interact with the smart contract on Klaytn Testnet Baobab.

Previous1. Project SetupNext3. Testing the contract using scripts

Last updated 1 year ago