使用JPA / ORM生成db模式是个坏主意吗？ [英] Is using JPA/ORM to generate a db schema a bad idea?

问题描述

Salve！

关于SO的其他问题/答案的一部分（以及声称相同的其他声明）：

Part of another question/answer on SO (as well as other statements claiming the same):

如果您通过JPA更新数据库架构（通常不是一个好习惯）

if you are updating your database schema by JPA (generally not a good practice though)

您是否应该使用JPA实现来生成数据库模式？

无论如何，我必须自己模拟实体和关系。我还需要定义约束，例如notnull，主键和外键，数据类型和大小。

I have to model the entities and relationships ony my own anyways. I need to define constraints such as notnull, primary and foreign keys, data types and sizes as well.

假设正在使用的JPA实现中没有任何缺陷DDL模式创建代码并且假设我确实正确地指定了所有JPA约束，关系等，JPA实现创建的db模式应该完全相同 - 如果不是更好 - 作为我自己手工制作的模式，对吧？

Assuming that the JPA implementation in use does not have any flaws in its DDL schema creation code and also assuming that I do specify all JPA constraints, relations etc. correctly, the db schema created by the JPA implementation should be exactly the same -if not better- as a schema handcrafted by myself, right?

这不包括特殊情况，例如（业务逻辑）特定的INSERT触发器等，因为这些根本不能由JPA实现生成（据我所知，如果我错了，请纠正我。

您对此有何看法？

我目前正在做什么首先手工编写我的db模式，然后设置JPA约束，关系等，让JPA实现也创建一个db模式。然后我比较两个模式，看看我是否正确完成了设置。这当然意味着我还必须指定与我手工模式相同的列名等。

What's your view on this?
I do currently handcraft my db schema first, then setup the JPA constraints, relations etc. and let the JPA implementation create a db schema as well. I then compare the two schemata to see whether I've done the setup correctly. This does of course mean that I also have to specify the same column names etc. as I did for my handcrafted schema.

使我的问题更加精确;我并不盲目信任ORM框架来为我生成架构。我宁愿知道模式在我的脑海中如何看待，然后配置框架以匹配它。

我想你可以手工创建更多/最有效的模式，但毕竟我需要（或者而是希望将它们与ORM框架一起使用。因此，虽然我不应该这样做，但我仍然需要在创建数据库模式时记住ORM框架的限制。

To make my question more precise; I do not blindly trust on the ORM framework to generate a schema for me. I rather have an idea of how the schema looks in my mind and then configure the framework to match it.
I guess you could create more/most efficient schemata only by hand, but after all I need (or rather want to) use them with an ORM framework. So while I should not do so, I need to keep the limitations of ORM frameworks in mind when creating a db schema anyways.

因为我按顺序使用ORM框架不必关心RDBMS细节，让我的应用程序使用RDBMS特定的DDL创建模式有什么意义？

如果我必须使用一些现有的和异国情调的模式，我不需要（重新）创建模式以及我可能无法使用这样的通用工具作为ORM框架。

So since I use an ORM framework in order not to have to care about RDBMS specifics, what's the point of having my application create the schema using RDBMS specific DDL?
If I have to use some existing and exotic schema I do not need to (re-)create the schema anways as well as I might not be able to use such a generic tool as an ORM framework.

推荐答案

我通常让JPA最初只创建架构。之后，我对其进行微调并手动维护。

I usually let JPA create the schema initially only. After, I fine-tune it and maintain it by hand.

有几个原因我更喜欢手工维护架构：

There are several reasons I prefer maintaining the schema by hand:

• 它允许在SQL代码中添加注释


• 它允许为表和列添加注释/描述


• 它允许指定表空间和JPA注释无法实现的其他东西


• 它允许在几个SQL文件之间分割模式（每个表一个+约束，一个用于约束，例如）


• 它允许我在模式迁移脚本中重用模式创建脚本的某些部分。例如，如果我的应用程序的第2版引入了3个新表，我需要一个可以重用创建三个新表的三个SQL文件的alter脚本


• 我有时需要使用序列的同义词而不是具体的


• 它让我选择主键约束的名称


• 可能还有其他一些我忘记的原因

• it allows putting comments in the SQL code
• it allows adding comments/descriptions for the tables and columns
• it allows specifying table spaces and other things that are not possible with JPA annotations
• it allows splitting the schema creation between several SQL files (one per table + one for the constraints, for example)
• it lets me reuse some parts of the schema creation script in my schema migration script. For example, if version 2 of my app introduces 3 new tables, I need an alter script that can reuse the three SQL files creating the three new tables
• I sometimes need to use synonyms for sequences, rather than concrete ones
• it lets me choose names for primary key constraints
• probably some other reasons I've forgotten

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