以太坊·食品溯源案例

本文节选自电子书《Netkiller Blockchain 手札》

Netkiller Blockchain 手札

本文作者最近在找工作，有意向致电 13113668890

Mr. Neo Chan, 陈景峯(BG7NYT)

中国广东省深圳市龙华新区民治街道溪山美地 518131

+86 13113668890 <netkiller@msn.com>

文档始创于2018-02-10

转载请与作者联系，转载时请务必标明文章原始出处和作者信息及本声明。

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内容摘要

这一部关于区块链开发及运维的电子书。

为什么会写区块链电子书？因为2018年是区块链年。

这本电子书是否会出版（纸质图书）？不会，因为互联网技术更迭太快，纸质书籍的内容无法实时更新，一本书动辄百元，很快就成为垃圾，你会发现目前市面的上区块链书籍至少是一年前写的，内容已经过时，很多例子无法正确运行。所以我不会出版，电子书的内容会追逐技术发展，及时跟进软件版本的升级，做到内容最新，至少是主流。

这本电子书与其他区块链书籍有什么不同？市面上大部分区块链书籍都是用2/3去讲区块链原理，只要不到 1/3 的干货，干货不够理论来凑，通篇将理论或是大谈特谈区块链行业，这些内容更多是头脑风暴，展望区块链，均无法落地实施。本书与那些书籍完全不同，不讲理论和原理，面向应用落地，注重例子，均是干货。

电子书更新频率？每天都会有新内容加入，更新频率最迟不会超过一周，更新内容请关注 https://github.com/netkiller/netkiller.github.io/commits/master

本文采用碎片化写作，原文会不定期更新，请尽量阅读原文。

http://www.netkiller.cn/blockchain/index.html

您的打赏是我的写作动力：http://www.netkiller.cn/blockchain/donations.html

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食品溯源案例

背景

需求是通过区块链跟踪产品，实现产品产地，生产，流通等环节溯源。

需求归纳，需要实现下面几点：

产品具备通用的属性，例如名称，价格，重量，颜色，体积等等

生产销售链条跟踪

涉及环节，农产品的供应链是一个非常复杂的过程，涉及多方，农业局、卫生局、药监局、工商局、环保局等多个部门交织其中。

合约设计

我们设计一个简单的合约

pragma solidity ^0.4.20;contract Trace {enum State { Origin, Factory, QA, Shipping, Received, Pending }string name;uint price;uint weight;bool lock = false;    //合约锁bool close = false;    //合约状态uint number = 1;uint attr_number = 1;mapping (address  => string) guestbook; //客户留言本    struct Attribute {address owner;    // 供应商string name;        // 属性的名字string date;        // 生产日期string desc;        // 描述信息}mapping (uint  => Attribute) attribute;struct Logistics {address owner;    // 中转站string date;    // 转运日期State status;   // 状态string message; // 留言信息}mapping (uint  => Logistics) stations;function Trace(string _name, uint _price, uint _weight) public {name = _name;price = _price;weight = _weight;}// 名称function getName() public view returns(string){return name;}// 价格function getPrice() public view returns(uint){return price;}// 重量function getWeight() public view returns(uint){return weight;}// 增加商品属性function putAttribute(address _owner,string _name, string _date, string _desc ) public{if(lock == false){Attribute memory item = Attribute(_owner, _name,_date,_desc);attribute[attr_number] = item;attr_number = attr_number + 1;}}// 获得属性function getAttribute(uint _attr_number) public view returns(address, string, string, string) {require(_attr_number < attr_number);Attribute memory item = attribute[_attr_number];return (item.owner, item.name, item.date, item.desc);}// 增加物流中转信息function putLogistics(address _owner,string _date, State _status, string _message ) public{if(close == false){Logistics memory node = Logistics(_owner,_date,_status,_message);stations[number] = node;number = number + 1;lock = true;}if (_status == State.Received) {close = true;}}// 获得中转信息function getLogistics(uint _number) public view returns(address, string, State, string) {require(_number < number);Logistics memory node = stations[_number];return (node.owner, node.date, node.status, node.message);}// 或者转中站数量function getLogisticsCount() public view returns(uint){return number;}// 客户留言function addGuestbook(address _owner, string message) public{guestbook[_owner] = message;}
}

怎样使用这个合约呢？

合约部署，需要输入三个参数，分别是名称，价格和装量

Trace(string _name, uint _price, uint _weight)

应用场景一

调用合约案例一，这是没有经过深加工的原产品案例。例如 Trace("山羊肉", 25, 50)

var contract;
Trace.deployed().then(function(instance){contract=instance;});
contract.getName();
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","颜色", "", "黑色")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","产地", "", "内蒙古")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","出生", "2017-01-12", "XXX牧场")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","宰杀", "2018-02-12", "XXX宰杀")contract.putLogistics("0x627306090abab3a6e1400e9345bc60c78a8bef57","2018-02-20",0,"XXX牧场");
contract.putLogistics("0x627306090abab3a6e1400e9345bc60c78a8bef57","2018-02-20",1,"XXX屠宰公司");
contract.putLogistics("0xc5fdf4076b8f3a5357c5e395ab970b5b54098fef","2018-02-22",2,"XXX检验检疫");
contract.putLogistics("0xf17f52151ebef6c7334fad080c5704d77216b732","2018-02-21",3,"XXX一级经销商");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-23",3,"XXX二级经销商");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-24",3,"XXX批发中心");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-25",3,"XXX超市");
contract.putLogistics("0x0d1d4e623d10f9fba5db95830f7d3839406c6af2","2018-02-26",4,"用户包裹收到");contract.getNode(); // 获得物流经过的转运站数量
应用场景二

调用合约案例二，经过深加工的原产品案例。

例如 Trace("牦牛肉干", 80, 500)

var contract;
Trace.deployed().then(function(instance){contract=instance;});
contract.getName();
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","调和油", "2016-10-10", "银龙鱼牌")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","辣椒粉", "2016-10-30", "西藏XXX公司生产")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","生抽", "2016-01-12", "XXX生抽，XXX生产")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","山梨酸钾", "2017-02-12", "XXX生产")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","防腐剂", "2017-02-12", "XXX生产")
contract.putAttribute("0x627306090abab3a6e1400e9345bc60c78a8bef57","牦牛肉", "2017-02-12", "XXX牧场")contract.putLogistics("0x627306090abab3a6e1400e9345bc60c78a8bef57","2018-02-20",0,"XXX牧场");
contract.putLogistics("0x627306090abab3a6e1400e9345bc60c78a8bef57","2018-02-20",1,"XXX公司生产");
contract.putLogistics("0xc5fdf4076b8f3a5357c5e395ab970b5b54098fef","2018-02-22",2,"XXX通过QA、QC");
contract.putLogistics("0xf17f52151ebef6c7334fad080c5704d77216b732","2018-02-21",3,"XXX一级经销商");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-23",3,"XXX二级经销商");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-24",3,"XXX批发中心");
contract.putLogistics("0x821aea9a577a9b44299b9c15c88cf3087f3b5544","2018-02-25",3,"XXX超市");
contract.putLogistics("0x0d1d4e623d10f9fba5db95830f7d3839406c6af2","2018-02-26",4,"用户包裹收到");contract.getNode(); // 获得物流经过的转运站数量

用户留言

contract.addGuestbook("0x0d1d423e623d10f9d10f9d10f9d10f9d10f9fba5","东西好吃，下次还买，给好评");

以上仅仅是作者的想法，这是一个学习和熟悉只能合约开发的例子，真实场景不太可行，因为以太坊无法处理高TPS的场景。