Категория: Last winner ethereum

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build ethereum app

Make the jump from React to Web3. A short, weekend project where you'll learn some Solidity, write + deploy a smart contract to the ETH blockchain. Learn about blockchain technology AND use Solidity to build your own Ethereum dApp. Create a crypto wallet and more. These are applications that focus on building out financial services using cryptocurrencies. They offer the likes of lending, borrowing, earning interest. ATHLETIC BILBAO VS REAL SOCIEDAD BETTING EXPERT BOXING

What would it look like for a user of our application to vote on the blockchain? Well, for starters, the user needs an account with a wallet address with some Ether, Ethereum's cryptocurrency. Once they connect to the network, they cast their vote and pay a small transaction fee to write this transaction to the blockchain.

Whenever the vote is cast, some of the nodes on the network, called miners, compete to complete this transaction. The miner who completes this transaction is awarded the Ether that we paid to vote. As a recap, when I vote, I pay a gas price to vote, and when my vote gets recorded, one of the computers on the network gets paid the my Ether fee. I in turn am confident my vote was recorded accurately forever. What is a Smart Contract? Well, the Ethereum blockchain allows us to execute code with the Ethereum Virtual Machine EVM on the blockchain with something called a smart contract.

Smart contracts are where all the business logic of our application lives. Smart contracts are in charge of reading and writing data to the blockchain, as well as executing business logic. Smart contacts are written in a programming language called Solidity , which looks a lot like Javascript. The function of smart contracts on the blockchain is very similar to a microservice on the web.

If the public ledger represents the database layer of the blockchain, then smart contracts are where all the business logic that transacts with that data lives. Also, they're called smart contracts because they represent a covenant or agreement. In the case of our voting dApp, it is an agreement that my vote will count, that other votes are only counted once, and that the candidate with the most votes will actually win the election.

Now let's jump in and start programming! We'll build a client-side application that will talk to our smart contract on the blockchain. This client-side application will have a table of candidates that lists each candidate's id, name, and vote count. It will have a form where we can cast a vote for our desired candidate.

It also shows the account we're connected to the blockchain with under "your account". Installing Dependencies The accompanying video footage for this portion of the tutorial begins at In order to build our dApp, we need a few dependencies first. It provides a suite of tools that allow us to write smart contacts with the Solidity programming language. It also enables us to test our smart contracts and deploy them to the blockchain.

It also gives us a place to develop our client-side application. You can install Ganache by downloading it from the Truffle Framework website. It will give us 10 external accounts with addresses on our local Ethereum blockchain. Each account is preloaded with fake ether. Metamask The next dependency is the Metamask extension for Google Chrome. In order to use the blockchain, we must connect to it remember, I said the block chain is a network.

Reference the video walk through if you get stuck! Syntax Highlighting The dependency is optional, but recommended. I recommend installing syntax highlighting for the Solidity programming language. Smoke Test - Step 1 The accompanying video footage for this portion of the tutorial begins at You can download the code for this portion of the tutorial here.

Feel free to use these as a reference point if you get stuck! First, find where you downloaded Ganache , and open it. Now that Ganache has booted, you have a local blockchain running. Ganache gave us 10 accounts preloaded with fake Ether this isn't worth anything on the main Ethereum network. Each account has a unique address and a private key. Each account address will serve as a unique identifier for each voter in our election.

We'll be using the Pet Shop box for this tutorial. We already have a Migration contract that handles our migrations to the blockchain. These migrations are similar to other web development frameworks that require migrations to change the state of a database.

Whenever we deploy smart contracts to the blockchain, we are updating the blockchain's state, and therefore need a migration. This smart contract will contain all the business logic of our dApp. It will be in charge reading from and write to the Ethereum blockchain.

It will allow us to list the candidates that will run in the election, and keep track of all the votes and voters. It will also govern all of the rules of the election, like enforcing accounts to only vote once. Open the file and start with the following code: pragma solidity 0. We start by declaring the solidity version with the pragma solidity statement.

Next, we declare the smart contract with the "contract" keyword, followed by the contract name. Next, we declare a state variable that will store the value of the candidate name. State variables allow us to write data to the blockchain. We have declared that this variable will be a string, and we have set its visibility to public.

Because it is public, solidity will give us a getter function for free that will allow us to access this value outside of our contract. We'll see that in action later in the console! Then, we create a constructor function that will get called whenever we deploy the smart contract to the blockchain.

This is where we'll set the value of the candidate state variable that will get stored to the blockchain upon migration. Notice that the constructor function has the same name as the smart contract. This is how Solidity knows that the function is a constructor.

Now that we've created the foundation for the smart contract, let's see if we can deploy it to the blockchain. In order to do this, we'll need to create a new file in the migrations directory. Next, we add it to the manifest of deployed contracts to ensure that it gets deployed when we run the migrations. From the console, run this code: Election. We retrieved a deployed instance of the contract with the deployed function, and assigned it to an app variable inside the promise's callback function.

This might look a little confusing at first, but you can reference the console demonstration in the video at for further explanation. Now we can read the value of the candidate variable like this: app. You've just written your first smart contract, deployed to the blockchain, and retrieved some of its data.

List Candidates - Step 2 The accompanying video footage for this portion of the tutorial begins at Now that everything is set up properly, let's continue building out the smart contact by listing out the candidates that will run in the election. We need a way to store multiple candidates, and store multiple attributes about each candidate. We want to keep track of a candidate's id, name, and vote count. Solidity allows us to create our own structure types as we've done for our candidate here.

We specified that this struct has an id of unsigned integer type, name of string type, and voteCount of unsigned integer type. Simply declaring this struct won't actually give us a candidate. We need to instantiate it and assign it to a variable before we can write it to storage. The next thing we need is a place to store the candidates. We need a place to store one of the structure types that we've just created.

We can do this with a Solidity mapping. A mapping in Solidity is like an associative array or a hash, that associates key-value pairs. This essentially gives us an id-based look up for each candidate. Since this mapping is assigned to a state variable, we will write data to the blockchain anytime we assign new key-value pairs to it. Next, we set this mapping's visibility to public in order to get a getter function, just like we did with the candidate name in the smoke test. That's because any key in a mapping that hasn't been assigned a value yet will return a default value an empty candidate in this case.

For example, if we only had 2 candidates in this election, and we try to look up candidate 99, then the mapping will return an empty Candidate structure. This behavior makes it impossible to know how many candidates exist, and therefore we must use a counter cache. Inside the function, we increment the candidate counter cache to denote that a new candidate has been added. Then we update the mapping with a new Candidate struct, using the current candidate count as the key. This Candidate struct is initialized with the candidate id from the current candidate count, the name from the function argument, and the initial vote count to 0.

Note that this function's visibility is private because we only want to call it inside the contract. You can follow along with me as I demonstrate this in the video at I'll leave that to you as an exercise. First, let me explain why testing is so important when you're developing smart contracts. We want to ensure that the contracts are bug free for a few reasons: 1. All of the code on the Ethereum blockchain is immutable; it cannot change. If the contract contains any bugs, we must disable it and deploy a new copy.

This new copy will not have the same state as the old contract, and it will have a different address. Deploying contracts costs gas because it creates a transaction and writes data to the blockchain. This costs Ether, and we want to minimize the amount of Ether we ever have to pay. If any of our contract functions that write to the blockchain contain bugs, the account who is calling this function could potentially waste Ether, and it might not behave the way they expect. Testing Now let's write some tests.

Make sure you have Ganache running first. These come bundled with the Truffle framework. We'll write all these tests in Javascript to simulate client-side interaction with our smart contract, much like we did in the console. First, we require the require the contract and assign it to a variable, like we did in the migration file.

You can write any arbitrary code inside this file and run it within your project. Client Side Development - configure your truffle project to host client side applications that talk to your smart contracts deployed to the blockchain. You can install Truffle with NPM in your command line like this. NOTE: It's important to use this exact version of truffle specified below in order to follow along with this tutorial.

Most major web browsers do not currently connect to blockchain networks, so we'll have to install a browser extension that allows them to do this. I'll the Metamask extension for Google Chrome. To install Metamask, visit this link or search for the Metamask Chrome plugin in the Google Chrome web store. Reference the video walk through if you get stuck! Metamask will also allow us to manage our personal account when we connect to the blockchain, as well as manage our Ether funds that we'll need to pay for transactions.

Project Setup The accompanying video footage for this portion of the tutorial begins at Now let's create the project! Your terminal output should show that the project was created successfully. You can open your text editor and see that some new files and directories were created once you ran that command.

Now let's create a package. We already have a Migration contract that handles our migrations to the blockchain. These migrations are similar to other web development frameworks that require migrations to change the state of a database. Whenever we deploy smart contracts to the blockchain, we are updating the blockchain's state, and therefore need a migration. Now let's start developing the smart contract that will manage our todo list.

We'll add all of the code for the smart contract inside of them. The thing we'll do is just keep track of the number of tasks inside the todo list. This will allow us to write some simple code that will help us ensure that the project is set up properly, and that our code is working on the blockchain.

Any data that we store inside this state variable is written to storage on the blockchain. It changes the smart contract's state, and has scope within the entire smart contract, as opposed to local variables which only have scope inside of functions. We can do this with a special modifier keyword called public in Solidity. When we do this, Solidity will magically create a taskCount function so that we can access this variable's value outside of the smart contract.

This will be useful when we are interacting with the smart contract in the console, from the client side application, and inside the test files. This file has many responsibilities, but two that I will highlight here: It contains the compiled bytecode version of the Solidity smart contract code that can be run on a the Ethereum Virtual Machine EVM , i. It contains a JSON representation of the smart contract functions that can be exposed to external clients, like client-side JavaScript applications.

Our next goal is to access the smart contract inside the Truffle console. However, we cannot run the Truffle console because our application is not yet connected to the Ganache personal blockchain network we set up in the dependencies section.

To talk to the smart contract on the personal blockchain network inside the Truffle console, we must do a few things: Update our project's configuration file to specify the personal blockchain network we want to connect to Ganache. Create a migration script that tells Truffle how to deploy the smart contract to the personal blockchain network.

Run the newly created migration script, deploying the smart contract to the personal blockchain network. First, we'll update the project configuration file to specify the personal blockchain network we want set up in the first section.

Find the file truffle-config. If you changed any settings inside the Ganache settings page, like the port, those should be reflected here. Next, we'll create a migration script inside the migrations directory to deploy the smart contract to the personal blockchain network. Any time we create a new smart contract, we are updating the state of the blockchain.

Remember, I said that a blockchain fundamentally is a database. Hence, whenever we permanently change it, we must migrate it from one state to another. This is very similar to a database migration that you might have performed in other web application development frameworks.

Notice that we number all of our files inside the migrations directory with numbers so that Truffle knows which order to execute them in. Next, we add it to the manifest of deployed contracts to ensure that it gets deployed when we run the migrations. We retrieved a deployed instance of the contract with the deployed function, and assigned it to an todoList. Also, note the use of the await keyword.

We must interact with the blockchain in an asynchronous fashion. Thus, JavaScript is an excellent choice for client-side interactions with blockchain smart contracts. There are several strategies for handling asynchronous actions in JavaScript. Truffle has recently released support for this inside the Truffle console. First, we can get the address of the smart contract that was deployed to the blockchain like this: todoList. You have done all of the following: Set up your machine for blockchain development Created a new truffle project Created your first smart contract Interacted with your newly created smart contract on a live blockchain If you got stuck on any of the steps, feel free to clone the project code for this section from github.

You can also reference the video tutorial for this section starting here. List Tasks The accompanying video footage for this portion of the tutorial begins at Now let's start listing out the tasks in the todo list. Here are all of the steps that we'll complete in this section: Write code to list tasks in the smart contract List tasks from the smart contract inside the Truffle console List tasks in the client side application Write a test for listing tasks In order to list the tasks inside the smart contract, we'll need a way to model a task in solidity.

Solidity allows you to define your own data types with structs. We can model any arbitrary data with this powerful feature. Note, that this does not represent an instance of a Task, but simply the definition of a Task struct. The lines contained in the curly braces define the attributes of the Task struct: uint id - this is the unique identifier for the struct.

It will have an id, just like a traditional database record. Note, we declare the data type for this identifiers as a uint, which stands for "unsigned integer". This simply means that it is a non-negative integer. It has no "sign", i. If it is true, the task will be "completed" or checked off from the todo list. Now that we've modeled a task, we need a place to put all of the tasks in the todo list!

We want to put them in storage on the blockchain so that the state of the smart contract will be persistent. We can access the blockchain's storage with with a state variable, just like we did with taskCount. We'll create a tasks state variable. It creates key-value pairs that get stored on the blockchain. We'll use a unique id as the key. The value will be the task it self. This will allow us to look up any task by id!

Now let's create a function for creating tasks. This will allow us to add new tasks to the todo list by default so that we can list them out in the console. We specify that this argument will be of string data type, and that it will persist in memory We set the function visibility to public so that it can be called outside of the smart contract, like in the console, or from the client side for example Inside the function, we create an id for the new task. We simply take the existing taskCount and increment it by 1.

Now we want to add one task to the todo list whenever the smart contract is deployed to the blockchain so that it will have a default task that we can inspect in the console. This function will get run only once, whenever the contract is initialized, i. Inside of this function, we have created one new default task with the string content "Check out dappuniversity. Now let's deploy this smart contract to the blockchain. In order to do this, we must deploy a new copy of our code. Remember, smart contract code is immutable!

It cannot change. Therefore, we must create a new smart contract any time we make code changes. Luckily Truffle provides a shortcut to assist with this. Now we have a new copy of the smart contract on the blockchain. Now let's list out the tasks in the console. This will allow us to access values from the tasks mapping by id.

You'll need to create the following files for your project: bs-config. We are using lite-server to serve all of the project files for the client side. We'll need to tell lite-server where all these files are located. We can do this by updating the browsersync configuration for lite-server inside the bs-config.

This will allow us to pull in any project dependencies like bootstrap into the client side with the vendor route, which we'll see momentarily. Now let's fill in HTML code for our todo list. I have commented-out the form code which we'll enable in a later section.

The file pulls in all of the dependencies for the project like the bootstrap templating framework that will allow us to create nice-looking UI elements without having to write too much CSS. It also uses the Truffle Conract library that will allow us to interact with the todo list smart contract wiht JavaScript. Now let's fill in the JavaScript code for this section.

We'll add code to the newly created app. We have created a new App object that contains all the functions we need to run the JavaScript app. I will explailn the important functions here. For full explanation, watch me explain the JavaScript code in the video at Also note that I have commented out a few lines of code that we will enable in later sections.

We configure web3 here. This is default web3 configuration specified by Metamask. Do not worry if you don't completely understand what is happening here. This is a copy-and-paste implementation that Metamask suggests. We create a JavaScript representation of the smart conract wit the Truffle Contract library. Then we load the smart contract data with web3. This will allow us to list the tasks in the todo list. Notice that we create a for loop to access each task individually.

That is because we cannot fetch the entire tasks mapping from the smart contract.

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