A Rails model has several ActiveRecord methods that make interacting with the database very simple. Models can be created, updated and destroyed very easily.
However, in some situations, one might want to mark a model as “readonly”. Meaning that only read operations are allowed — no updates or deletions. A situation like this may occur in the middle of a big refactoring. A model has been retired but we may not be ready to wipe it out. We might still need to read it.
Before
This can be achieved by adding a readonly?
method to the class which returns true?
.
class Rocket
...
def readonly?
true
end
end
Now, when we try to update or delete the model we get an error.
irb(main):001:0> rocket.update name: "A1"
TRANSACTION (5.4ms) BEGIN
User Load (6.2ms) SELECT `users`.* FROM `users` WHERE `users`.`id` = ? LIMIT ? [["id", 1], ["LIMIT", 1]]
TRANSACTION (1.8ms) ROLLBACK
Traceback (most recent call last):
/Users/swaathi/.rbenv/versions/2.7.5/lib/ruby/gems/2.7.0/bundler/gems/rails-08af60e01dcf/activerecord/lib/active_record/persistence.rb:1147:in `_raise_readonly_record_error': Rocket is marked as readonly (ActiveRecord::ReadOnlyRecord)
irb(main):002:0> rocket.destroy
Traceback (most recent call last):
/Users/swaathi/.rbenv/versions/2.7.5/lib/ruby/gems/2.7.0/bundler/gems/rails-08af60e01dcf/activerecord/lib/active_record/persistence.rb:1147:in `_raise_readonly_record_error': Rocket is marked as readonly (ActiveRecord::ReadOnlyRecord)
Both options raise the ActiveRecord::ReadOnlyRecord
error.
However when we try to touch the model we get no error.
irb(main):002:0> rocket.touch
TRANSACTION (0.5ms) BEGIN
Rocket Update (14.2ms) UPDATE `rockets` SET `rockets`.`updated_at` = '2022-08-14 06:40:24.291104' WHERE `rockets`.`id` = 1
TRANSACTION (5.6ms) COMMIT
=> true
While a touch
call doesn’t do much damage,
the update_columns
call does.
Unfortunately, marking a model as readonly
does not prevent us from updating the model in all possible ways.
This corrupts the data with unwarranted updates.
After
People were too quick to point out this discrepancy, however, the Rails team was even quicker to issue a patch!
A simple update to the update_columns
and touch
models within ActiveRecord fixed this.
activerecord/lib/active_record/persistence.rb
...
module ActiveRecord
module Persistence
extend ActiveSupport::Concern
module ClassMethods
def update_columns
...
_raise_readonly_record_error if readonly?
...
end
end
end
end
Now readonly models are no longer updated when update_columns
or touch
is called.