# 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.

<pre><code><strong>$ npm install -g truffle
</strong></code></pre>

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.

<pre><code><strong>$ tree
</strong>.
├── contracts
├── migrations
├── test
└── truffle-config.js

4 directories, 1 file
</code></pre>

Create a KVStore contract with the following command.

```
$ truffle create contract KVStore
```

The KVStore.sol file is created as shown below.

<pre><code><strong>// SPDX-License-Identifier: MIT
</strong>pragma solidity >=0.4.22 &#x3C;0.9.0;

contract KVStore {
  constructor() public {
  }
}
</code></pre>

## 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.

<pre><code><strong>/**
</strong><strong> ...
</strong><strong> */
</strong><strong>require('dotenv').config();
</strong><strong>// const { MNEMONIC, PROJECT_ID } = process.env;
</strong><strong>const { PRIVATE_KEY } = process.env;
</strong>
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"
      }
    }
  },
</code></pre>

## 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
```