数据库/表的重组

Question

假设我有一个包含这些表的数据库

Car --> Has Dealerships --> Has Demographic --> Has Revenue

在推出后，客户说他们希望汽车有型号，每个型号都应该有经销商

所以我的结构变成了

Car --> Has Model --> Has Dealerships --> has Demographic --> Has Revenue

我如何迁移到第二个数据库结构？我需要在Car和Dealership之间切断外键才能使用。我是否只是拍摄旧数据库的快照，并在知道如何处理它的上下文中编写一个包装器？

Answer 1

我的理解是它应该是Model --> Has Cars，而不是Car --> Has Model。在我看来，-->指定更加一致。

因此，正确的最终关系链可能看起来像这样：

Model --> Has Cars
      --> Has Dealerships --> Has Demographic --> Has Revenue

我会想象以下一系列动作：

1. 创建并填充Models表。此时您的架构：

   Model
   
   Car --> Has Dealerships --> Has Demographic --> Has Revenue
   

2. 向ModelID添加Cars列，并根据您的业务需求使用正确的Models引用填充该列。它会给你以下结果：

   Model --> Has Cars --> Has Dealerships --> Has Demographic --> Has Revenue
   

3. 向ModelID添加Dealerships引用，通过使用当前关系将Dealerships加入Cars来填充该引用。您最终会在Dealerships和Models，直接和Cars之间建立双重关系，如下所示：

   Model      -->     Has Dealerships --> Has Demographic --> Has Revenue
       \               /
        \-> Has Cars -/
   

4. 删除Cars --> Dealership外键，删除Dealerships.CarID引用列。这将是您的最终结果：

   Model --> Has Dealerships --> Has Demographic --> Has Revenue
       \
        \--> Has Cars