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问题描述

无处不在 > 互联网人士提到，使用default_scope轨道是个坏主意，default_scope在stackoverflow上的热门话题是关于如何覆盖它的信息.这感觉很混乱，值得提出一个明确的问题(我认为).

Everywhere on the internet people mention that using the rails default_scope is a bad idea, and the top hits for default_scope on stackoverflow are about how to overwrite it. This feels messed up, and merits an explicit question (I think).

所以:为什么反对使用default_scope导轨?

So: why is using the rails default_scope recommended against?

问题1

让我们考虑一下基本示例:

Problem 1

Lets consider the basic example:

class Post < ActiveRecord::Base
  default_scope { where(published: true) }
end

设置默认值published: true的动机可能是确保要显示未发布的(私人)帖子时必须明确显示您的信息.到目前为止一切顺利.

The motivation to make the default published: true, might be to make sure you have to be explict when wanting to show unpublished (private) posts. So far so good.

2.1.1 :001 > Post.all
  Post Load (0.2ms)  SELECT "posts".* FROM "posts"  WHERE "posts"."published" = 't'

这几乎是我们所期望的.现在让我们尝试:

Well this is pretty much what we expect. Now lets try:

2.1.1 :004 > Post.new
 => #<Post id: nil, title: nil, published: true, created_at: nil, updated_at: nil>

这是默认范围的第一个大问题:

And there we have the first big problem with default scope:

=> default_scope将影响您的模型初始化

=> default_scope will affect your model initialization

在这种模型的新创建实例中，将反映default_scope.因此，尽管您可能希望确保不要偶然列出未发布的帖子，但现在您默认创建默认发布的帖子.

In a newly created instance of such a model, the default_scope will be reflected. So while you might have wanted to be sure to not list unpublished posts by chance, you're now creating published ones by default.

考虑一个更详细的示例:

Consider a more elaborate example:

class Post < ActiveRecord::Base
  default_scope { where(published: true) }
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :posts
end

让我们获得第一个用户的帖子:

Lets get the first users posts:

2.1.1 :001 > User.first.posts
  Post Load (0.3ms)  SELECT "posts".* FROM "posts"  WHERE "posts"."published" = 't' AND "posts"."user_id" = ?  [["user_id", 1]]

这看起来像预期的一样(请确保一直滚动到右侧，以查看有关user_id的部分).

This looks like expected (make sure to scroll all the way to the right to see the part about the user_id).

现在，我们要获取所有帖子的列表-包括未发布的内容-对已登录用户的视图说.您将意识到必须覆盖"或撤消" default_scope的效果.快速浏览Google之后，您可能会发现有关unscoped的信息.看看接下来会发生什么:

Now we want to get the list of all posts - unpublished included - say for the logged in user's view. You'll realise you have to 'overwrite' or 'undo' the effect of default_scope. After a quick google, you'll likely find out about unscoped. See what happens next:

2.1.1 :002 > User.first.posts.unscoped
  Post Load (0.2ms)  SELECT "posts".* FROM "posts"

=> Unscoped会删除通常可能适用于您选择的所有范围，包括(但不限于)关联.

有多种方法可以覆盖default_scope的不同效果.正确处理将使非常复杂，我会认为不使用首先，这将是一个更安全的选择.

There are multiple ways to overwrite the different effects of the default_scope. Getting that right gets complicated very quickly and I would argue not using the default_scope in the first place, would be a safer choice.

这篇关于为什么经常建议使用rails default_scope?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

sure

为什么经常建议使用rails default_scope?

问题描述

推荐答案

问题1

Problem 1