Embarking on a journey into the world of blockchain, this tutorial serves as your compass to navigate the intricate process of data storage on the Ethereum network. With Python as our scripting language, Truffle as our development framework, and Ganache as our personal blockchain, we’ll explore the steps necessary to securely and efficiently persist data. This guide is crafted to empower developers with the tools and insights needed to harness the full potential of Ethereum’s decentralized capabilities. Join us as we delve into the practical aspects of blockchain data storage, a skill set that is becoming increasingly vital in the digital age.
1. Project Setup: Laying the Foundation
Embark on your blockchain development journey by setting up the cornerstone of your project. Begin by opening the HelloWorld.sol file, which will house your smart contract. This initial step involves adding a few lines of code that lay the groundwork for your contract’s functionality. By doing so, you’re not just writing code; you’re crafting the blueprint for your decentralized application on the Ethereum blockchain. Follow along as we inject life into HelloWorld.sol, transforming it from a mere file into a gateway for blockchain interaction.
1. Setting Up Your Project
Begin by opening HelloWorld.sol and make the following additions:
pragma solidity >= 0.5.0;
contract HelloWorld {
string public payload;
function setPayload(string memory content) public {
payload = content;
}
function sayHello() public pure returns (string memory) {
return 'Hello World!';
}
}Spin Up Truffle Local Blockchain: Use the Truffle Develop CLI to start the local blockchain environment.$ truffle develop
Now, we need to update our contract, what under Truffle's Suite is performed with the migrate command. Write migrate within Truffle's console.setPayload deployed at 0x85534E0ec31b63d635CcBa1fb6b953a9C47a9022 (contract address). Write this address somewhere else, we will need it soon.We can verify that the contract was properly updated by fetching the contract instance and checking for
setPayload method existence, as well as the value of payload variable:2. Executing a transaction
When we call a function that only returns a value, such as sayHello, the blockchain state is not altered. Since now we want to save a value to the blockchain, its state must be altered and it is done via a transaction execution.
We want to execute this transaction from our Python script, the same we used for calling the sayHello method in the previous post.
Add the following to the bottom of app.py:
# executes setPayload function
tx_hash = contract.functions.setPayload('abc').transact()
# waits for the specified transaction (tx_hash) to be confirmed
# (included in a mined block)
tx_receipt = web3.eth.waitForTransactionReceipt(tx_hash)
print('tx_hash: {}'.format(tx_hash.hex()))
Also, update the deployed_contract_address in app.py with the new contract address (output from migrate). If you don't remember it, go back to the Truffle console and call instance.address.
On another terminal session, execute our Python script:
python app.py
Hello World!
tx_hash: 0x2b7bf989fd0fc692d0ef976b3293c39958ab7de64a08a3f66c0d758b871ad8e6
Not fun, right? How do we know that the data was persisted? Go back to the Truffle console and call payload variable:
$ truffle(develop)> instance.payload.call()
'abc' # cool! It changed!
This means that our transaction was mined, thus being added to a block that was successfully added to the blockchain.
3. Inspecting the blockchain with Ganache
There are various ways for inspecting the blockchain. For example, using the Truffle console:
# Fetch blockchain's latest mined block
$ truffle(develop)> block = await web3.eth.getBlock("latest")
$ truffle(develop)> block
{
number: 6, # YMMV
(...)
transactions: [
'0x2b7bf989fd0fc692d0ef976b3293c39958ab7de64a08a3f66c0d758b871ad8e6'
]
}
transactions lists all the transactions that were added to this block. In this case, there is one transaction that should match tx_hash that was printed when we ran app.py.
To make our lives easier, there is a GUI tool for inspecting the blockchain and its transactions: Ganache. As per their website:
Quickly fire up a personal Ethereum blockchain which you can use to run tests, execute commands, and inspect state while controlling how the chain operates.
After successfully installing and opening it, you should see the following image:
Select "Quickstart" and you'll be welcomed with a screen listing some accounts and its respective addresses (very similar to how truffle develop works). There will be also a RPC Server address, such as http://127.0.0.1:8545, write that down. Click "Save" (top-right corner) so this Ganache workspace is persisted.
When quick-starting Ganache, it created another local blockchain for us. We can now tell truffle to use Ganache's blockchain (which has a nice UI). To do so, open truffle-config.js and replace it with the following:
module.exports = {
networks: {
development: {
// host and port should match the RPC Server address
// as seen in Ganache
host: "127.0.0.1",
port: 8545,
network_id: "*"
}
}
};
Go to the Contracts tab, and select Link Truffle Projects. Click Add Project then select the truffle-config.js file from hello-eth/ root project folder. Click Save and Restart at the upper-right corner.
If you go to the Contracts tab now, you should see two contracts:
- HelloWorld: Not Deployed
- Migrations: Not Deployed
Open another terminal session, go to the project root level (where truffle-config.js is located), and type truffle migrate. It will deploy our contracts to Ganache's blockchain. Copy the HelloWorld contract address and update the deployed_contract_address in app.py with its new value, as well as the variable blockchain_address with http://127.0.0.1:8545.
- blockchain_address = 'http://127.0.0.1:9545' # truffle blockchain
+ blockchain_address = 'http://127.0.0.1:8545' # ganache blockchain
- deployed_contract_address = '0x85534E0ec31b63d635CcBa1fb6b953a9C47a9022'
+ deployed_contract_address = '0x433D7E91B659CB4f1bbBb8dacd2B1cBBa7F82F1A'
Under Contracts tab now, both contracts (HelloWorld and Migrations) should have an address. It means they're deployed! woohoo!
Now, run app.py again to execute a new transaction on our newest blockchain and then click on HelloWorld contract:
Notice the TX HASH, it should be the same as printed when you ran app.py.
And if you click on the transaction itself:
You can see both the function that was called and the inputs.
Run app.py a few more times, change abc (in tx_hash = contract.functions.setPayload('abc').transact()) to something else, then inspect your contract again. It's YOUR blockchain now, act up to it!
If something is not clear or if there are any suggestions, please leave a comment below!
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