价值对象如何存储在数据库中? [英] How are Value Objects stored in the database?

问题描述

我还没有真正看到任何示例，但是我假设它们已保存在数据库内的包含实体表中.

即.如果我有一个Person实体/集合根和一个对应的Person表，如果它具有一个名为Address的值对象，则地址值将保存在此Person表中！

这对我拥有其他拥有公司地址的其他实体(例如公司等)的域名有意义吗?

(我目前正在编写一个项目管理应用程序，并尝试使用DDD)

解决方案

出于您所描述的原因，可以将Value Objects存储在单独的表中.但是，我认为您对实体与VO误解了-这与持久性无关.

这是一个例子:

假设公司和人员都具有相同的邮件地址.这些语句中的哪一个被认为是有效的?

1. "如果我修改Company.Address，我要 要自动获取的Person.Address 这些变化"
2. "如果我修改Company.Address， 不得影响Person.Address"

如果 1 为true，则地址应该是 实体 ，因此具有自己的表

如果 2 为true，则地址应为 值对象 .它可以作为组件存储在父实体表中，也可以具有自己的表(更好的数据库规范化).

如您所见，地址的持久化与实体/VO语义无关.

I haven't really seen any examples, but I assume that they are saved inside the containing entity table within the database.

Ie. If I have a Person entity/aggregate root and a corresponding Person table, if it had a Value Object called Address, Address values would be saved inside this Person table!

Does that make sense for a domain where I have other entities such as Companies etc. that have an Address?

(I'm currently writing a project management application and trying to get into DDD)

解决方案

It's ok to store Value Objects in a separate table, for the very reasons you've described. However, I think you're misunderstanding Entities vs VOs - it's not a persistence related concern.

Here's an example:

Assume that a Company and Person both have the same mail Address. Which of these statements do consider valid?

1. "If I modify Company.Address, I want Person.Address to automatically get those changes"
2. "If I modify Company.Address, it must not affect Person.Address"

If 1 is true, Address should be an Entity, and therefore has it's own table

If 2 is true, Address should be a Value Object. It could be stored as a component within the parent Entity's table, or it could have it's own table (better database normalisation).

As you can see, how Address is persisted has nothing to do with Entity/VO semantics.

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