The following project is a small decentralized application that basically showcases the use of blockchain as a secondary data base alongside an offchain database with MongoDB. The application consists in a login using smart contracts, which means using truffle contracts in the backend.
The usage of blockchain as a secondary database is the following: every time a user sings in in the login, after knowing the user is valid according to MongoDB registry, the hash of the login input is compared to blockchain's registry and only if this is validated, the user is able to access safely.
NodeJS version: 10.15.3
express version: 4.17.1
express-handlebars version: 3.1.0
express-session version: 1.16.2
mongodb version: 2.2.33
truffle-contract version: 4.0.31
web3 version: 1.2.1
ganache-cli version: 6.7.0
The folder node_modules was uploaded to this repo because if you try to install web3 using npm, you might encounter some bug in certain web3 packages and it might not work. That is why I suggest to download this full folder from here as well.
After downloading this repo to your local directory, the next thing to do is to download Ganache Quickstart for desktop version. Once installed, turn on your Ganache environment (click on Quickstart).
Turn on MongoDB service. Search for services inside your computer. Right click on MongoDB Server and choose Start.
Go to Windows Powershell, and enter to the project's folder. Once there, type: truffle console --network ganache to enter Truffle Console. Then, type migrate --compile-all --reset to compile the Smart contracts (do this everytime you change a contract). This also delets any registry in the blockchain. Finally, type .exit to exit the console.
Now, start the server. Type npm start on your Powershell. This is equivalent to typing node ./bin/www. On this file, you will see the port for the project is 3000.
You will see first the login page. On the bottom, the MongoDB registry of users will be displayed. In this case, the users will start in zero, like below.
Whenever you reset all contracts, you should click on Restart DB to empty the MongoDB registry just as the Ganache one. They should have the same amount of users.
If you click on Register, you will be able to type the username and password of a new user, like below. Keep in mind that only the super user can add a new user, and this is validated by the blockchain using the account hash of whoever is calling the new user transaction.
When you confirm the new user, you get redirected to the login page, where you will be able to see the new user's info down below. All this is just for proof of concept.
If you sign in as the new user, you will enter the main page, given the validation using the blockchain hash registry.
Here, you can choose to see the Transaction Information by clicking on Audit button. This will take you to the following page, which shows the corresponding user registration information that was stored when the blockchain added the user.
This info should coincide with the Ganache Quickstart info. If you click on the transaction by recognizing the hash, you will see the info:
You can also click on the Register button and add another user again. Users displayed on the bottom parts are updated using Ajax calls every 3 seconds.
Finally, you can access the Blockchain Market where you will be able to sell and buy items. Access looks like the following:
To stop the server, go to Powershell and type Ctrl + C.
The language for smart contracts in this dapp is Solidity. To add a smart contract, first create a file using .sol extension in the contracts folder. Write your code in Solidity and then, go to the file migrations/2_deploy_contracts.js and use the function deployer.deploy() as with the other contracts.
The file routes/index.js is where most of the backend's smart contract use is done.
The Market section uses Metamask for the account notifications.