rails 使用default_scope遇到的问题以及解决方案

1.使用default_scope

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

2.1.1 :001 > Post.all

  Post Load (0.2ms)  SELECT "posts".* FROM "posts"  WHERE "posts"."published" = 1

2.使用default_scope需要小心的问题

　一、

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

　

二、

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

class User < ActiveRecord::Base
  has_many :posts
end



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]]

三、使用假删除的时候，要注意unscoped的使用，unscope 会取消所有的scope, 包括deleted_at

3. 取消default scope   unscoped的使用

　

class User < ActiveRecord::Base
  default_scope { where tester: false }
  scope :testers, -> { unscope(:where).where tester: true }
  scope :with_testers, -> { unscope(:where).where tester: [true, false] }
  # ...
end

eg：

Foo.unscope(where: :bar)
or

scope :not_default, -> { unscope(where: :bar) }

Foo.not_default

It is currently possible to unscope stuff like: :where，:select, :group, :order, :lock, :limit, :offset, :joins, :includes, :from, :readonly, :having.

But still please avoid using of default_scope if you can. It's for your own good.

参考链接：

   　　https://stackoverflow.com/questions/1834159/overriding-a-rails-default-scope

          https://www.thinbug.com/q/25087336