# Sample Contracts
## Install Truffle development environment
Truffle is an environment where smart contracts can be developed and tested on blockchains that use Ethereum Virtual Machine (EVM) like Metadium.
### Requirements
To use Truffle, Node.js v14 - v18 must be installed in Windows, Linux, or macOS environments.
### Install Truffle
Install Truffle using NPM in your terminal.
$ npm install -g truffle
To check the installation of Truffle, run the following command:
```
$ truffle version
Truffle v5.11.5 (core: 5.11.5)
Ganache v7.9.1
Solidity - 0.8.21 (solc-js)
Node v18.19.0
Web3.js v1.10.0
```
## Create project
Create a new directory for your new Truffle project. We will create a smart contract that implements key/value storage in the example. To do this, we create a directory called KVStore.
```
$ mkdir KVStore
$ cd KVStore
```
Initialize the Truffle project.
```
$ truffle init
Starting init...
================
> Copying project files to /Users/trident/Projects/DApp/KVstore/Temp
Init successful, sweet!
Try our scaffold commands to get started:
$ truffle create contract YourContractName # scaffold a contract
$ truffle create test YourTestName # scaffold a test
http://trufflesuite.com/docs
```
The following directories and files are created.
$ tree
.
├── contracts
├── migrations
├── test
└── truffle-config.js
4 directories, 1 file
Create a KVStore contract with the following command.
```
$ truffle create contract KVStore
```
The KVStore.sol file is created as shown below.
// SPDX-License-Identifier: MIT
pragma solidity >=0.4.22 <0.9.0;
contract KVStore {
constructor() public {
}
}
## Writing a smart contract
Create a set function that stores Key/Value and a get function that uses Key to read the stored values as follows.
```
// SPDX-License-Identifier: MIT
pragma solidity >=0.4.22 <0.9.0;
contract KVStore {
mapping(string => string) store;
function get(string memory key) public view returns(string memory) {
return store[key];
}
function set(string memory key, string memory value) public {
store[key] = value;
}
}
```
## Setup
To compile and deploy, modify the truffle-config.js file.
First, wallet configuration is required. To avoid exposing the Private Key in the code, use dotenv and store the PRIVATE\_KEY in the .env file as follows. If you use dotenv, install it using the npm i dotenv command to avoid compilation errors.
```
PRIVATE_KEY=["YOUR_PRIVATE_KEY"]
```
Second, proceed with network configuration. To use the Metadium Testnet, add the network configuration as follows.
```
metadium_testnet: {
provider: ()=> new HDWalletProvider(PRIVATE_KEY, "https://api.metadium.com/dev"),
network_id: 12,
gasPrice: 80000000000
}
```
Finally, proceed with compiler configuration. In the example, version 0.8.21 is used, and the optimizer is configured.
/**
...
*/
require('dotenv').config();
// const { MNEMONIC, PROJECT_ID } = process.env;
const { PRIVATE_KEY } = process.env;
const HDWalletProvider = require('@truffle/hdwallet-provider');
module.exports = {
...
networks: {
...
metadium_testnet: {
provider: ()=> new HDWalletProvider(PRIVATE_KEY, "https://api.metadium.com/dev"),
network_id: 12,
gasPrice: 80000000000
}
},
...
compilers: {
solc: {
version: "0.8.21", // Fetch exact version from solc-bin (default: truffle's version)
// docker: true, // Use "0.5.1" you've installed locally with docker (default: false)
settings: { // See the solidity docs for advice about optimization and evmVersion
optimizer: {
enabled: true,
runs: 200
},
evmVersion: "byzantium"
}
}
},
## Smart contract compile
```
truffle compile
Compiling your contracts...
===========================
> Compiling ./contracts/KVStore.sol
> Artifacts written to /Users/trident/Projects/DApp/KVstore/Temp/build/contracts
> Compiled successfully using:
- solc: 0.8.21+commit.d9974bed.Emscripten.clang
```
## Smart contract deployment
Before deploying smart contracts, create a script file named 1\_deploy\_contracts.js in the migrations directory as follows:
```
ar KVStore = artifacts.require("KVStore");
module.exports = function(deployer) {
deployer.deploy(KVStore);
};
```
Deploy the contract with the truffle migrate command.
```
truffle migrate --network metadium_testnet
Starting migrations...
======================
> Network name: 'metadium_testnet'
> Network id: 12
> Block gas limit: 105000000 (0x6422c40)
1_deploy_contracts.js
=====================
Deploying 'KVStore'
-------------------
> transaction hash: 0x1039d819b825a80281d27ae737858579752192b642e0678902570c64791739b0
> Blocks: 2 Seconds: 4
> contract address: 0x4981bEF8190D4CC385e4b0DcE67Faf24347dbB87
> block number: 50419826
> block timestamp: 1707187839
> account: 0xcf3C2104DF83d92C845d71Be6354266b222295aD
> balance: 10.443230699997734106
> gas used: 322126 (0x4ea4e)
> gas price: 80 gwei
> value sent: 0 ETH
> total cost: 0.02577008 ETH
> Saving artifacts
-------------------------------------
> Total cost: 0.02577008 ETH
Summary
=======
> Total deployments: 1
> Final cost: 0.02577008 ETH
```
---
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