Apparently dependent => destroy is ignored when also using the :through option.
So I have this...
class Comment < ActiveRecord::Base
has_many :comment_users, :dependent => :destroy
has_many :users, :through => :comment_users
...
end
...but deleting a Comment does not result in the associated comment_user records getting deleted.
What's the recommended approach, then, for cascade deletes when using :through?
Thanks
Apparently :dependent is not ignored!
The real issue was that I was calling Comment.delete(id) which goes straight to the db, whereas I now use Comment.destroy(id) which loads the Comment object and calls destroy() on it. This picks up the :dependent => :destroy and all is well.
The original poster's solution is valid, however I wanted to point out that this only works if you have an id column for that table. I prefer my many-to-many tables to only be the two foreign keys, but I had to remove my "id: false" from the migration table definition for cascading delete to work. Having this functionality definitely outweighs not having an id column on the table.
If you have a polymorphic association, you should do what #blogofsongs said but with a foreign_key attribute like so:
class User < ActiveRecord::Base
has_many :activities , dependent: :destroy, foreign_key: :trackable_id
end
Related
I render a set of checkboxes and I want to delete all the Privilege of a User.
When I check one of the checkboxes, a record is created.
When I uncheck one of the checkboxes, a record is deleted.
I have searched all the questions related, but unluckily none works.
Rails 5.2.3
User
has_many :user_privileges, class_name: 'UserPrivileges'
has_many :privileges, through: :user_privileges
Privilege
has_many :user_privileges, class_name: 'UserPrivileges'
has_many :users, through: :user_privileges
UserPrivileges
belongs_to :user
belongs_to :privilege
The issue kick in when I want to delete ( uncheck ) the last privilege-record of that user in the join_table.
The record is still there, and there is no way to delete/destroy that specific record.
My intuition recall to the callbacks, I have tried different ways of using dependent but the last record is still there.
Any tips are welcome.
Thanks
If you want to delete the record from the join table, you need to add dependent: :destroy to has_many :through relationship.
# privilege.rb
has_many :user_privileges, class_name: 'UserPrivileges'
has_many :users, through: :user_privileges, dependent: :destroy
See What gets deleted? in API docs:
There is a potential pitfall here: has_and_belongs_to_many and
has_many :through associations have records in join tables, as well as
the associated records. So when we call one of these deletion methods,
what exactly should be deleted?
The answer is that it is assumed that deletion on an association is
about removing the link between the owner and the associated
object(s), rather than necessarily the associated objects themselves.
So with has_and_belongs_to_many and has_many :through, the join
records will be deleted, but the associated records won't.
To run dependent: :destroy callback, you must use the destroy or destroy_all method when deleting the privilege record.
See Delete or destroy? in API docs:
For has_many, destroy and destroy_all will always call the destroy
method of the record(s) being removed so that callbacks are run.
However delete and delete_all will either do the deletion according to
the strategy specified by the :dependent option, or if no :dependent
option is given, then it will follow the default strategy. The default
strategy is to do nothing (leave the foreign keys with the parent ids
set), except for has_many :through, where the default strategy is
delete_all (delete the join records, without running their callbacks).
class Post < ActiveRecord::Base
has_many :posts_tags
has_many :tags, through: :posts_tags
end
class PostsTag < ActiveRecord::Base
belongs_to :post
belongs_to :tag
end
class Tag < ActiveRecord::Base
has_many :posts_tags
has_many :posts, through: :posts_tags
end
When Post gets destroyed I want all of its associations to Tag deleted as well. I do NOT want validations on PostsTag model to run. I just want to deleted.
I've found that adding a dependent on the relationship to posts tags from the Post model works as I want: has_many :posts_tags, dependent: :delete_all.
However, the documentation on the subject seems to suggest that I should do this instead: has_many :tags, through: :posts_tags, dependent: :delete_all. When I do this, the Tag object gets destroyed and the join object remains.
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#method-i-has_many
For has_many, destroy will always call the destroy method of the record(s) being removed so that callbacks are run. However delete will either do the deletion according to the strategy specified by the :dependent option, or if no :dependent option is given, then it will follow the default strategy. The default strategy is :nullify (set the foreign keys to nil), except for has_many :through, where the default strategy is delete_all (delete the join records, without running their callbacks).
How can I have the default strategy actually used? If I leave :dependent off completely, no records are removed at all. And I cannot just indicate :dependent on a has_many relationship. Rails comes back and says "The :dependent option expects either :destroy, :delete_all, :nullify or :restrict ({})".
If I don't specify :dependent on either of the relationships, it does NOT nullify the post_id on the PostsTag object as it seems to suggest
Perhaps I am reading this wrong and the approach that I found works is the correct way?
Your original idea of:
has_many :posts_tags, dependent: :delete_all
is exactly what you want. You do not want to declare this on the has-many-though association :tags, as that will destroy all associated Tags. What you want to delete is the association itself - which is what the PostTag join model represents.
So why do the docs say what they do? You are misunderstanding the scenario that the documentation is describing:
Post.find(1).destroy
Post.find(1).tags.delete
The first call (your scenario) will simply destroy the Post. That is, unless you specify a :dependent strategy, as I suggest you do. The second call is what the documentation is describing. Calling .tags.delete will not (by default) actually destroy the tags (since they are joined by has-many-through), but the associated join model that joins these tags.
I have a simple has_many/belongs_to association between 2 of my models.
My problem is that when I delete an object that I no longer want (from the parent model), the foreign key within the child model's object remains. For example:
Forest
has_many :trees, :inverse_of => :forest
Tree
belongs_to :forest
When I delete a Forest object, all the associated Tree objects still contain a value for forest_id, which results in errors on the frontend. Is there some sort of hook like before_destroy that I can use? Though I'm thinking there's probably a very simple solution to this.
Thanks
I think that you want the :dependent option.
has_many :trees, :inverse_of => :forest, :dependent => :nullify
This will set the foreign keys to nil when the associated model is destroyed. You could also use :dependent => :destroy to destroy the model.
The documentation here might help.
You have add the :dependent option with the association like
has_many :trees, :dependent => :destroy
It will delete all trees of a particular Forest object.
Callbacks on objects which are updated during removal from a relationship collection don't seem to be executing for me.
I have a model EntityLocation which serves as a polymorphic relationship between Entities (Users/Places/Things) and Locations (Zips, Addresses, Neighborhoods).
class EntityLocation < ActiveRecord::Base
belongs_to :entity, :polymorphic => true
belongs_to :location, :polymorphic => true
def after_save
if entity_id.nil? || location_id.nil?
# Delete me since I'm no longer associated to an entity or a location
destroy
end
end
end
For this example, lets assume that I have a "Thing" with a collection of "Locations", referenced by my_thing.locations. This returns a collection of Zip, Address, etc.
If I write the code
my_thing.locations = [my_thing.locations.create(:location => Zip.find(3455))]
then as expected a new EntityLocation is created and can be accurately referenced from my_thing.locations. However the problem is that the records which were previously contained within this collection are now orphaned in the database with a nil entity_id attribute. I'm trying to delete these objects in the after_save callback, however it's never getting executed on the old object.
I've also tried using an after_update, and after_remove and neither gets called on the old record. The newly created record after_save callback does get called as expected, but that doesn't help me.
Does Rails update the previously referenced object without executing the callback chain through active record? All ideas appreciated. Thank you.
Why does this need to be polymorphic? It seems that you could simply use has_many :through to model the many-to-many relationship.
Secondly, why not simply delete the join table row through the association with :dependent => :destroy? Then you don't need a custom callback
class Entity < ActiveRecord::Base
has_many :entity_locations, :dependent => :destroy
has_many :locations, :through => :entity_locations
end
class EntityLocation < ActiveRecord::Base
belongs_to :entity
belongs_to :location
end
class Location < ActiveRecord::Base
has_many :entity_locations, :dependent => :destroy
has_many :entities, :through => :entity_locations
end
Now deleting from either side deletes the join table row as well.
I was following the screencast on rubyonrails.org (creating the blog).
I have following models:
comment.rb
class Comment < ActiveRecord::Base
belongs_to :post
validates_presence_of :body # I added this
end
post.rb
class Post < ActiveRecord::Base
validates_presence_of :body, :title
has_many :comments
end
Relations between models work fine, except for one thing - when I delete a post record, I'd expect RoR to delete all related comment records. I understand that ActiveRecords is database independent, so there's no built-in way to create foreign key, relations, ON DELETE, ON UPDATE statements. So, is there any way to accomplish this (maybe RoR itself could take care of deleting related comments? )?
Yes. On a Rails' model association you can specify the :dependent option, which can take one of the following three forms:
:destroy/:destroy_all The associated objects are destroyed alongside this object by calling their destroy method
:delete/:delete_all All associated objects are destroyed immediately without calling their :destroy method
:nullify All associated objects' foreign keys are set to NULL without calling their save callbacks
Note that the :dependent option is ignored if you have a :has_many X, :through => Y association set up.
So for your example you might choose to have a post delete all its associated comments when the post itself is deleted, without calling each comment's destroy method. That would look like this:
class Post < ActiveRecord::Base
validates_presence_of :body, :title
has_many :comments, :dependent => :delete_all
end
Update for Rails 4:
In Rails 4, you should use :destroy instead of :destroy_all.
If you use :destroy_all, you'll get the exception:
The :dependent option must be one of [:destroy, :delete_all, :nullify,
:restrict_with_error, :restrict_with_exception]