Soft deletes for ActiveRecord done right.
A simple ActiveRecord mixin to add conventions for flagging records as discarded.
Add this line to your application's Gemfile:
gem 'discard', '~> 1.2'And then execute:
$ bundle
Declare a record as discardable
Declare the record as being discardable
class Post < ActiveRecord::Base
include Discard::Model
endYou can either generate a migration using:
rails generate migration add_discarded_at_to_posts discarded_at:datetime:index
or create one yourself like the one below:
class AddDiscardToPosts < ActiveRecord::Migration[5.0]
def change
add_column :posts, :discarded_at, :datetime
add_index :posts, :discarded_at
end
endPost.all # => [#<Post id: 1, ...>]
Post.kept # => [#<Post id: 1, ...>]
Post.discarded # => []
post = Post.first # => #<Post id: 1, ...>
post.discard # => true
post.discard! # => Discard::RecordNotDiscarded: Failed to discard the record
post.discarded? # => true
post.undiscarded? # => false
post.kept? # => false
post.discarded_at # => 2017-04-18 18:49:49 -0700
Post.all # => [#<Post id: 1, ...>]
Post.kept # => []
Post.discarded # => [#<Post id: 1, ...>]From a controller
Controller actions need a small modification to discard records instead of deleting them. Just replace destroy with discard.
def destroy
@post.discard
redirect_to users_url, notice: "Post removed"
endpost = Post.first # => #<Post id: 1, ...>
post.undiscard # => true
post.undiscard! # => Discard::RecordNotUndiscarded: Failed to undiscard the record
post.discarded_at # => nilFrom a controller
def update
@post.undiscard
redirect_to users_url, notice: "Post undiscarded"
endUnder paranoia, soft deleting a record will destroy any dependent: :destroy
associations. Probably not what you want! This leads to all dependent records
also needing to be acts_as_paranoid, which makes restoring awkward: paranoia
handles this by restoring any records which have their deleted_at set to a
similar timestamp. Also, it doesn't always make sense to mark these records as
deleted, it depends on the application.
A better approach is to simply mark the one record as discarded, and use SQL joins to restrict finding these if that's desired.
For example, in a blog comment system, with Posts and Comments, you might
want to discard the records independently. A user's comment history could
include comments on deleted posts.
Post.kept # SELECT * FROM posts WHERE discarded_at IS NULL
Comment.kept # SELECT * FROM comments WHERE discarded_at IS NULLOr you could decide that comments are dependent on their posts not being
discarded. Just override the kept scope on the Comment model.
class Comment < ActiveRecord::Base
belongs_to :post
include Discard::Model
scope :kept, -> { undiscarded.joins(:post).merge(Post.kept) }
def kept?
undiscarded? && post.kept?
end
end
Comment.kept
# SELECT * FROM comments
# INNER JOIN posts ON comments.post_id = posts.id
# WHERE
# comments.discarded_at IS NULL AND
# posts.discarded_at IS NULLSQL databases are very good at this, and performance should not be an issue.
In both of these cases restoring either of these records will do right thing!
It's usually undesirable to add a default scope. It will take more effort to work around and will cause more headaches. If you know you need a default scope, it's easy to add yourself ā¤.
class Post < ActiveRecord::Base
include Discard::Model
default_scope -> { kept }
end
Post.all # Only kept posts
Post.with_discarded # All Posts
Post.with_discarded.discarded # Only discarded postsIf you're migrating from paranoia, you might want to continue using the same column.
class Post < ActiveRecord::Base
include Discard::Model
self.discard_column = :deleted_at
endCallbacks can be run before, after, or around the discard and undiscard operations. A likely use is discarding or deleting associated records (but see "Working with associations" for an alternative).
class Comment < ActiveRecord::Base
include Discard::Model
end
class Post < ActiveRecord::Base
include Discard::Model
has_many :comments
after_discard do
comments.discard_all
end
after_undiscard do
comments.undiscard_all
end
endWarning: Please note that callbacks for save and update are run when discarding/undiscarding a record
discard_all and undiscard_all is intended to behave like destroy_all which has callbacks, validations, and does one query per record. If performance is a big concern, you may consider replacing it with:
scope.update_all(discarded_at: Time.current)
or
scope.update_all(discarded_at: nil)
A common use case is to apply discard to a User record. Even though a user has been discarded they can still login and continue their session. If you are using Devise and wish for discarded users to be unable to login and stop their session you can override Devise's method.
class User < ActiveRecord::Base
def active_for_authentication?
super && !discarded?
end
end- Special handling of AR counter cache columns - The counter cache counts the total number of records, both kept and discarded.
- Recursive discards (like AR's dependent: destroy) - This can be avoided using queries (See "Working with associations") or emulated using callbacks.
- Recursive restores - This concept is fundamentally broken, but not necessary if the recursive discards are avoided.
Discard provides the smallest subset of soft-deletion features that we think are useful to all users of the gem. We welcome the addition of gems that work with Discard to provide additional features.
- discard-rails-observers integrates discard with the rails-observers gem
I've worked with and have helped maintain paranoia for a while. I'm convinced it does the wrong thing for most cases.
Paranoia and acts_as_paranoid both attempt to emulate deletes by setting a column and adding a default scope on the model. This requires some ActiveRecord hackery, and leads to some surprising and awkward behaviour.
- A default scope is added to hide soft-deleted records, which necessitates
adding
.with_deletedto associations or anywhere soft-deleted records should be found. š- Adding
belongs_to :child, -> { with_deleted }helps, but doesn't work for joins and eager-loading before Rails 5.2
- Adding
deleteis overridden (really_deletewill actually delete the record) šdestroyis overridden (really_destroywill actually delete the record) šdependent: :destroyassociations are deleted when performing soft-destroys š±- requiring any dependent records to also be
acts_as_paranoidto avoid losing data. š¬
- requiring any dependent records to also be
There are some use cases where these behaviours make sense: if you really did want to almost delete the record. More often developers are just looking to hide some records, or mark them as inactive.
Discard takes a different approach. It doesn't override any ActiveRecord methods and instead simply provides convenience methods and scopes for discarding (hiding), restoring, and querying records.
You can find more information about the history and purpose of Discard in this blog post.
After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.
Please consider filing an issue with the details of any features you'd like to see before implementing them. Discard is feature-complete and we are only interested in adding additional features that won't require substantial maintenance burden and that will benefit all users of the gem. We encourage anyone that needs additional or different behaviour to either create their own gem that builds off of discard or implement a new package with the different behaviour.
Discard is very simple and we like it that way. Creating your own clone or fork with slightly different behaviour may not be that much work!
If you find a bug in discard, please report it! We try to keep up with any issues and keep the gem running smoothly for everyone! You can report issues here.
The gem is available as open source under the terms of the MIT License.
- Ben Morgan who has done a great job maintaining paranoia
- Ryan Bigg, the original author of paranoia (and many things), as a simpler replacement of acts_as_paranoid
- All paranoia users and contributors
![dependabot[bot] avatar](https://avatars.githubusercontent.com/in/29110?v=4 "dependabot[bot]")
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent