0
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这个错觉
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根源之一
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可能是关系数据库
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我们拿刚才那个植物来说
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你看
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左上角是类图
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类图可能映射数据库里面，可能得到这样的数据库结构
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你看
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植物ID，ID，ID
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你看这里面
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植物的这个数据是分散在
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各个表里面的，对不对
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所以呢，你看，这个可不就是根吗
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这个不就是根吗
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对吧
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但这是什么
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这是数据库里面的
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存放的方式
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从对象的概念上
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它是一个整体
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不是说植物对象是个根
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不是，植物对象是一个整体
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它不是根
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刚才我们也讲了
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你把那个部件都扔掉了
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剩下就没有了
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00:01:07,363 --> 00:01:09,921
剩下除了标识，什么都没有了
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对不对
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35
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所以呢，有可能是关系数据库带来的一种错觉
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第二个错觉的根源，可能是来自我们
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人类社会的观察
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在人类社会中
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比如说，我们
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我们是作为一个人
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对不对
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所以呢，我们看到的
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各种东西
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它是以人的角度来看的
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比如说
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我们经常有一个
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组织上的一个视角
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大家可能
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看过我《软件方法》这个书
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我们说，要有组织视角
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什么组织视角
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比如说
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某某企业
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找某某税务局
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干嘛
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办税
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或者说
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项目部，就像这个，项目部
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找财务部
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这是两个部门
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对吧
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每个部门各有各自责任
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项目部
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要求财务部结算
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临时工的工资
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这是两个组织之间的
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协作
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项目部要求财务部结算工资
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但是的话
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我们作为人去观察
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实际上并没有办法观察到
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有一个巨人叫项目部
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他向财务部喊一声
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哎
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财务部，你给我结算工资，没有的
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我们会观察到什么样子
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项目部里面有个人
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有个生命体
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比如说，项目部的经理
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他向另外一个生命体
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财务部经理
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发出请求，哎
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那个
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张经理，给我们结算
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我们部门的临时工的工资
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对不对
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这个时候，你看
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我们就会有什么
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聚合根的错觉
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这个项目部经理就是这个
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项目部的聚合根
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财务部经理就是财务部的聚合根
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因为我们的社会是人类社会
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公司
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还有政府机构等等
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是没有什么
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它是没有生命的
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它是由人组成的，对吧
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但是
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面向对象的世界里面
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对象是有生命的
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如果说，有一个部门对象
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那边也有一个部门对象
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两个互相发消息就可以了
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不需要人
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不需要说，有一个经理这样
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因为
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里面的对象
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我们就假设它是有生命的
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并不需要人
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实际上怎么样
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我们目前绝大多数的系统
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所描述的对象
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在现实世界中
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绝大多数是没有生命的
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比如说，订单、设备
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车辆、房间，等等
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有生命的
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像人、动物、植物
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这种是非常少的
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因为我们的软件系统
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描述的是什么
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人类的大脑
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对这个宇宙的万事万物的认识
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把人类的大脑对宇宙的万事万物认识
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把它封装到我们的软件里面
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当然，封装完了
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就可以
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用来取代
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这个人的思考了
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104
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那你想想，我们人
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这个领域
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人的生命体或者生命
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这个领域
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在整个宇宙万事万物里
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占多少比例
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对不对
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占不了多少的
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而且我们目前的绝大多数的系统
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还管不到这么深
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因为我们对人体的认识
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对生命的认识
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并没有那么深
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肯定没有对地球的认识
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对
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宇宙，太阳什么的认识深
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对不对
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你没有认识，你封装什么呀
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对吧
123
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所以这是第二点
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这是我猜测的
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为什么会有这样的错觉
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这是我们说的聚合根的
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最大的问题
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根本就不存在的
129
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对不对
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那其他问题
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我们下次再说了
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包括里面的
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00:05:33,400 --> 00:05:35,596
他用葡萄做隐喻
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实际上这个是错的
135
00:05:37,133 --> 00:05:39,550
背后可能有知识误区
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还有，他用了一个词，相关联的对象
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这个用词也是有问题的
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背后也可能有知识误区
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第三点
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聚合
141
00:05:54,230 --> 00:05:57,850
或者说要建立整体-部分的关系
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我们要从逻辑的角度来思考
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而不是说从持久化
144
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从性能角度思考
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那就是思维颠倒了
146
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对不对
147
00:06:09,030 --> 00:06:11,778
我们上次说到思维颠倒
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有个视频说过了
149
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现在很多人就这样干
150
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我决定把A和B
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00:06:19,330 --> 00:06:19,646
152
00:06:19,646 --> 00:06:20,910
当成
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聚合
154
00:06:21,888 --> 00:06:24,450
当成整体-部分的关系
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为什么呀
156
00:06:25,620 --> 00:06:28,293
因为我决定在持久化的时候
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我们以它们作为一个单元
158
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这不是思维颠倒吗
159
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对不对
160
00:06:36,050 --> 00:06:37,960
那不就是我们之前说的那个
161
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A跟B是泛化关系
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为什么
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因为我代码都写好了
164
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你看，代码都写好了
165
00:06:49,050 --> 00:06:50,821
A扩展B，A继承B嘛
166
00:06:50,821 --> 00:06:52,790
所以它不是泛化关系嘛
167
00:06:54,680 --> 00:06:55,686
那不就是什么
168
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你拍脑袋
169
00:06:56,491 --> 00:06:57,900
先把代码写好了
170
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然后再从代码来
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反证这个逻辑，不对的
172
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那这个我们后面
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174
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再说
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那感兴趣，想事先了解的同学
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可以下载这个电子书
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178
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里面我都有写了