智能合约自学笔记之三买家区块链之以太坊

其实除了买家后面还有，不过我看了一会实在是放弃了，因为是个全栈视频，web相关我实在是不行了，因为js我真是一点都不会。教程中用react库，在web上链接到ganache这个虚拟区块链上，同时metamask也获取ganache数据显示出来，最后全栈为用户提供了web接口，这就是全部过程。最有意思的是，这个系统所有的调用都用的js，只有脚本用的solidity。脚本用的面向对象，其实面向对象长得都一样，我用C++的底子完全可以理解。这就是我学会的东西。我在网上看到还有用其它语言写合约的。
其实我想学会的是设计dapp，而smart contract只是二代区块链，教程的题目也是dapp university。不过仔细想一下，web不管是调用smart contract还是dapp，效果都是一样的，只不过smart contract需要付钱，dapp不需要付钱，再有些其它的修改罢了，我理解为dapp只是在smart contract的应用场景上多了一些，本质没有太大变化。
下面尽快学习网络和操作系统的基本知识，保证工作能做好，后续是搞js还是换语言搞dapp还是怎么样，再说吧，该定计划了蓝莓侠
合约

// the file is for creating smart contract pragma solidity ^0.5.0; contract Marketplace { //state variable string public name; mapping(uint => Product) public products; //key and value,id and smartcontract uint public productCount = 0; //solidity dosen't has size function for mappingstruct Product { uint id; //unique string name; uint price; address payable owner; bool purchased; } event ProductCreated( uint id, string name, uint price, address payable owner, bool purchased ); event ProductPurchased( uint id, string name, uint price, address payable owner, bool purchased ); constructor() public { name = "Dapp University Marketplace"; } function createProduct(string memory _name, uint _price) public{ //Make sure parameters are correct require(bytes(_name).length > 0); require(_price > 0); //Increment product count productCount++; //因为productCount初始值为0,所以这个要放在创建product之前 // Createthe product,将新建的product加入哈希中 products[productCount] = Product(productCount, _name, _price, msg.sender, false); //msg是个全局变量，sender就是调用ganache的那个用户，也就是谁调创建这个合约，msg.sender就是谁 //Trigger an event emit ProductCreated(productCount, _name, _price, msg.sender, false); } //<按照id将product从协议中提出来，修改后再放回去，这样可以保证原子性，智能合约肯定要考虑并发的 function purchaseProduct(uint _id) public payable { // Fetch the product Product memory _product = products[_id]; // Fetch the owner address payable _seller = _product.owner; // Make sure the product has a valid id require(_product.id > 0 && _product.id <= productCount); // Require that there is enough Ether in the transaction require(msg.value >= _product.price); // Require that the product has not been purchased already require(!_product.purchased); // Require that the buyer is not the seller require(_seller != msg.sender); // Transfer ownership to the buyer _product.owner = msg.sender; // Mark as purchased _product.purchased = true; // Update the product products[_id] = _product; // Pay the seller by sending them Ether address(_seller).transfer(msg.value); // Trigger an event emit ProductPurchased(productCount, _product.name, _product.price, msg.sender, true); }}

【智能合约自学笔记之三买家】调用过程

//it's for calling smartcontract const Marketplace = artifacts.require('./Marketplace.sol') //import the contract into the test file, of course the smartcontact is defined in this filerequire('chai') .use(require('chai-as-promised')) .should()contract('Marketplace', ([deployer, seller, buyer]) =>{ let marketplace before(async () => { marketplace = await Marketplace.deployed()//deployed这个函数是异步的，await关键字为了将异步变为同步 }) describe('deployment', async() => { //mocha which is a framework of js it('deploys successfully', async()=> { const address = await marketplace.address assert.notEqual(address, 0x0) //chai for assert assert.notEqual(address, null) assert.notEqual(address, '') assert.notEqual(address, undefined) })it('has a name', async() => { const name = await marketplace.name() assert.equal(name, 'Dapp University Marketplace') }) }) describe('products', async() => { //mocha which is a framework of js let result, productCountbefore(async () => { result = await marketplace.createProduct('iPhone X', web3.utils.toWei('1','Ether'),{from:seller })//使用的时候都是用的wei为单位，但是因为wei特别的小，IPHONEX价格为2以太币比较合适，就用个转换函数 productCount = await marketplace.productCount() }) it('creates products', async() => { // success assert.equal(productCount, 1) const event = result.logs[0].args assert.equal(event.id.toNumber(), productCount.toNumber(), 'id is correct') assert.equal(event.name, 'iPhone X', 'name is correct') assert.equal(event.price, '1000000000000000000', 'price is correct') assert.equal(event.owner,seller ,'owner is correct') assert.equal(event.purchased,false,'purchased is correct') // FAILURE: Product must have a name await await marketplace.createProduct('', web3.utils.toWei('1', 'Ether'), { from: seller }).should.be.rejected; // FAILURE: Product must have a price await await marketplace.createProduct('iPhone X', 0, { from: seller }).should.be.rejected; })it('lists products', async() => { const product= await marketplace.products(productCount) assert.equal(product.id.toNumber(), productCount.toNumber(), 'id is correct') assert.equal(product.name, 'iPhone X', 'name is correct') assert.equal(product.price, '1000000000000000000', 'price is correct') assert.equal(product.owner,seller ,'owner is correct') assert.equal(product.purchased,false,'purchased is correct') })it('sells products', async () => { // Track the seller balance before purchase let oldSellerBalance oldSellerBalance = await web3.eth.getBalance(seller) oldSellerBalance = new web3.utils.BN(oldSellerBalance)// SUCCESS: Buyer makes purchase result = await marketplace.purchaseProduct(productCount, { from: buyer, value: web3.utils.toWei('1', 'Ether')})// Check logs const event = result.logs[0].args assert.equal(event.id.toNumber(), productCount.toNumber(), 'id is correct') assert.equal(event.name, 'iPhone X', 'name is correct') assert.equal(event.price, '1000000000000000000', 'price is correct') assert.equal(event.owner, buyer, 'owner is correct') assert.equal(event.purchased, true, 'purchased is correct')// Check that seller received funds let newSellerBalance newSellerBalance = await web3.eth.getBalance(seller) newSellerBalance = new web3.utils.BN(newSellerBalance)let price price = web3.utils.toWei('1', 'Ether') price = new web3.utils.BN(price)const exepectedBalance = oldSellerBalance.add(price)// assert.equal(newSellerBalance.toString(), exepectedBalance.toString())// FAILURE: Tries to buy a product that does not exist, i.e., product must have valid id await marketplace.purchaseProduct(99, { from: buyer, value: web3.utils.toWei('1', 'Ether')}).should.be.rejected; // FAILURE: Buyer tries to buy without enough ether // FAILURE: Buyer tries to buy without enough ether await marketplace.purchaseProduct(productCount, { from: buyer, value: web3.utils.toWei('0.5', 'Ether') }).should.be.rejected; // FAILURE: Deployer tries to buy the product, i.e., product can't be purchased twice await marketplace.purchaseProduct(productCount, { from: deployer, value: web3.utils.toWei('1', 'Ether') }).should.be.rejected; // FAILURE: Buyer tries to buy again, i.e., buyer can't be the seller await marketplace.purchaseProduct(productCount, { from: buyer, value: web3.utils.toWei('1', 'Ether') }).should.be.rejected; }) })})