在文档数据库中继承？ [英] inheritance in document database?

问题描述

我想知道，因为我搜索的pdfxxx确定指南和开始xxx为单词继承，但我没有找到什么？我错过了什么？因为我用hibernate和mysql做了一个tablePerHierarchy继承，在xxx中是否会因为某种原因而弃用？

（用你不喜欢的数据库替换xxx ）

解决方案

我知道这个回答有点晚了，但对于MongoDB，你可能看起来有些不同。 / p>

Mongo是无模式的，因此tablePerHierarchy的概念不一定有用。

p>

  class A 
属性X 
属性Y 
属性Z 
 
类B继承自A 
属性W 
  

在RDMS中，你可能会有这样的

 表A：列X，Y，Z 
表B：列X，Y，Z，W 
  

但MongoDB没有模式。所以你不需要这样结构数据。相反，你将有一个集合包含所有类型A或B（或C ...）的对象（或文档）。

是这样的一系列对象：

  {_ id：1，X：1，Y ：2，Z：3} 
 {_id：2，X：5，Y：6，Z：7，W：6} 
  

你会注意到我在类型B的对象的旁边存储类型A的对象。MongoDB使这很容易。

但是，如果你有数据对象或实体

  {_ id：1，type： A，X：1，Y：2，Z：3} 
 {_id：2，type：B，X：5，Y ：6，Z：7，W：6} 
  

编写用于加载对象的工厂类。

i am wondering because i searched the pdf "xxx the definitive guide" and "beginning xxx" for the word "inheritance" but i didn't find anything? am i missing something? because i am doing a tablePerHierarchy inheritance with hibernate and mysql, does that become deprecated for some reason in xxx?

(replace xxx with the "not only sql" database you like)

解决方案

I know this answer is a little late, but for MongoDB, you're probably looking at something slightly different.

Mongo is schemaless, so the concept of "tablePerHierarchy" is not necessarily useful.

Assume the following

class A
  property X
  property Y
  property Z

class B inherits from A
  property W

In an RDMS you would probably have something like this

table A: columns X, Y, Z
table B: columns X, Y, Z, W

But MongoDB does not have a schema. So you do not need to structure data in this way. Instead, you would have a "collection" containing all objects (or "documents") of type A or B (or C...).

So your collection would be a series of objects like this:

{"_id":"1", "X":1, "Y":2, "Z":3}
{"_id":"2", "X":5, "Y":6, "Z":7, "W":6}

You'll notice that I'm storing objects of type A right beside objects of type B. MongoDB makes this very easy. Just pull up a Document from the Collection and it "magically" has all of the appropriate fields/properties.

However, if you have "data objects" or "entities", you can make your life easier by adding a type.

{"_id":"1", "type":"A", "X":1, "Y":2, "Z":3}
{"_id":"2", "type":"B", "X":5, "Y":6, "Z":7, "W":6}

This makes it easier to write a factory class for loading your objects.

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