Rails:schema.rb 有什么作用? [英] Rails: what does schema.rb do?

问题描述

我以前认为Rails项目中的db/schema.rb存储的是数据库schema，这样ActiveRecord就能知道什么表/column 它有.

I used to think the db/schema.rb in a Rails project stored the database schema, so that ActiveRecord can know what table/column it has.

但早些时候我惊讶地发现我的项目在删除db/schema.rb后正常运行！

But earlier I surprisingly noticed that my project runs normally after I delete db/schema.rb!

那么，既然 Rails 可以在没有它的情况下工作，那么 schema.rb 到底能做什么?

So, since the Rails can work without it, what does schema.rb really do?

推荐答案

schema.rb 主要有两个目的:

1. 它记录了数据库模式的最终当前状态.通常，尤其是当您有多个迁移时，很难仅从迁移中推断出模式.有了现有的 schema.rb，你可以看看那里.ActiveRecord 本身确实不会使用它.它将在运行时内省数据库，因为这比期望用户保持 schema.rb 最新更安全.但是，为了避免混淆您的开发人员，您应该始终维护一个与您的迁移保持同步的文件.

1. It documents the final current state of the database schema. Often, especially when you have more than a couple of migrations, it's hard to deduce the schema just from the migrations alone. With a present schema.rb, you can just have a look there. ActiveRecord itself will indeed not use it. It will introspect the database during runtime as this is much safer than to expect users to keep the schema.rb up-to-date. However to avoid confusion of your developers, you should always maintain a file that is up-to-date with your migrations.

测试使用它来填充数据库架构.因此，rake db:schema:dump 通常作为 rake test:prepare 运行的一部分运行.目的是测试数据库的模式与当前的开发数据库完全匹配.

It is used by the tests to populate the database schema. As such a rake db:schema:dump is often run as part of the rake test:prepare run. The purpose is that the schema of the test database exactly matches the current development database.

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