We have two Rails models: Person and Administrator. We're disallowing removal of Administrators at the model level:
class Person < ActiveRecord::Base
end
class Administrator < Person
def destroy
raise "Can't remove administrators."
end
end
me = Administrator.new
me.destroy # raises an exception
I'd like to be able to get around this during testing, but only for specific instances created during setup and teardown. I don't want to change the behavior of the class, so class_eval and remove_method aren't feasible.
I tried to redefine the actual instance's #destroy method:
def me.destroy
super
end
or redefine it on the singleton class:
class << me
def destroy
super
end
end
but those still raised the exception. I couldn't figure out how to get it to call the superclass method implicitly. I ended up creating my own destroy! method (since that's not actually a method in ActiveRecord), which sort of violates my desire not to change the behavior of the class:
def destroy!
ActiveRecord::Persistence.instance_method(:destroy).bind(self).call
end
Is there any simple way to tell a single instance method to call its superclass method?
Final Answer: Based on the article Holger Just linked to, I was able to simply call the superclass method explicitly:
def me.destroy
self.class.superclass.instance_method(:destroy).bind(self).call
end
I'd try to refactor the behavior to be more test-friendly. E.g. you could allow an optional parameter to destroy e.g. i_know_what_im_doing that has to be set to true to carry out the destroy. Alternatively you could cancel the destroy with a before_destroy hook like
class Administrator < Person
def before_destroy(record)
# You can't destroy me
false
end
end
In your tests, you can then call Administrator.skip_callback :before_destroy to ignore it and to have a proper destroy.
Finally, you could overwrite / stub the method in your tests. While you say you don't want to modify the class's behavior, you still have to do that (and implicitly do that with your destroy! method today).
I'm not familiar with Ruby metaprograming, so I wont answer if you can a call a method of the super class on an instance without modifying it. But you can create a hook to a superclass method with alias :
class Administrator < Person
alias :force_destroy :destroy
def destroy
raise "Can't remove administrators."
end
end
With this, admin.destroy will raise an exception, but admin.force_destroy will actually call the ActiveRecord destroy.
Related
I have a method current_org that's defined simply as:
def current_org
Organization.find_by(subdomain: Apartment::Tenant.current)
end
It's always the same, whether it's in a view, controller, a model, or even a service. Since the current tenant is derived from the database connection, I shouldn't have to worry about it being properly scoped. And I find myself using it everywhere.
What's the best way to define a global method in Rails so I can just call current_org from anywhere? Currently my best solution is defining a module in /lib and calling it with CustomHelperMethods.current_org. But I'm looking for something a little cleaner.
I'd put it as a class method in an Organiation model or create a special service/class that fetches it.
class Organization < ApplicationRecord
def self.current_org
find_by(subdomain: Apartment::Tenant.current)
end
end
or
# e.g. in app/services/
class CurrentOrganization
def self.current_org
Organization.find_by(subdomain: Apartment::Tenant.current)
end
end
Is it possible to overwrite a method and still fallback to the original method (given no superclass is involved)?
def User
def method
# do some original stuff
end
def method
# do some new stuff
call_the_original :method
end
end
Hopefully, my specific example will make my meaning more clear.
Using activestorage has_one_attached :avatar in a User model adds a setter method. I want to do some stuff when this setter is called, but I still want the original method to run.
class User
has_one_attached :avatar
# According to the source (see references) this mixes in the following setter method
def avatar=(attachable)
# do activestorage stuff
end
# I want to add some custom functions to this, before still running "do activestorage
# stuff". I could copy, paste and edit the entire function. But out of interest,
# I wondered if a more elegant solution exists.
def avatar=(attachable)
# do my stuff
super(attachable)
end
end
super obviously does not work because User is not inheriting from anything in which avatar=() is defined.
I could create e.g. MasterUser class containing has_one_attached and from which User inherits, but this seems overkill for just this particular case.
I could submit to a custom_avatar_method=(attachable) which calls avatar=(attachable).
But with this question what I'm really interested in is whether there a way to call a previously defined method from a method of the same name?
References:
#has_one_attached source
You can make use of alias_method to access the previous definition here:
class User
def avatar=(attachable)
# do activestorage stuff
end
alias_method :original_avatar=, :avatar=
def avatar=(attachable)
# do my stuff
self.original_avatar=(attachable)
end
end
Another option is saving the old method inside a variable before defining the new method with the same name. Then call the variable from inside the newly defined method:
class User
def avatar=(attachable)
# do activestorage stuff
end
instance_method(:avatar=).tap do |avatar_eq|
define_method(:avatar=) do |attachable|
# do my stuff
avatar_eq.bind(self).call(attachable)
end
end
end
In the above example define_method(:avatar=) has to be used, since a regular def avatar= wont let you access the avatar_eq variable.
The code is somewhat more complicated than JagdeepSinghs answer, but leaves the class less cluttered with methods. The old method is no longer defined and thus can no longer be called by itself.
References:
Module#instance_method to get the previously defined method
Object#tap to namespace a variable to a small portion of the class definition
Module#define_method to define the new method with the same name
UnboundMethod#bind to bind the unbound method to the current User instance
Method#call to call the bound previously defined method
# app/models/product.rb
class Product < ApplicationRecord
def self.method1(param1)
# Here I want to call method2 with a parameter
method2(param2)
end
def method2(param2)
# Do something
end
end
I call method1 from controller. When I run the program. I got an error:
method_missing(at line method2(param2))
.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/activerecord-5.0.0/lib/active_record/relation/batches.rb:59:in `block (2 levels) in find_each
...
class Product < ApplicationRecord
def self.method1(param1)
# Here I want to call method2 with a parameter
method2(param2)
end
def self.method2(param2)
# Do something
end
end
Explanation: first one is a class method, the latter was an instance method. Class methods don't need a receiver (an object who call them), instance methods need it. So, you can't call an instance method from a class method because you don't know if you have a receiver (an instanciated object who call it).
It does not work because method2 is not defined for Product object.
method2 is an instance method, and can be called only on the instance of Product class.
Of course #Ursus and #Andrey Deineko answers are right solution of this problem. Besides that, if anyone want to know how we can call instance method with in class method(though this is not actually class method in ruby) for those self.new.instance_method.
I have a user model in my application. Now I want to replace some user model coding into 2 categories likely employ.rb and customer.rb under a module users, to avoid more number of codes in a single model. I want to access a method send_mail in customer.rb after a user created.
user.rb
after_create:send_msg_on_order
def send_msg_on_order
Users::Customer.send_mail
end
users/customer.rb
def send_mail
Mailer.send_mail_to_customer.deliver
end
And I am getting undefined method `send_mail' for Users::Customer:Module error.
You have defined send_mail method as instance method but calling it as a class method. Either make it a class method or create an instance of Customer model and call it.
Making the method a class method:
def self.send_mail
Mailer.send_mail_to_customer.deliver
end
If you wish to keep it an instance method, then call it like this:
after_create:send_msg_on_order
def send_msg_on_order
Users::Customer.new.send_mail
end
HTH
You can also call like this
def send_msg_on_order
Customer.send_mail
end
I've been having this bothering recurring theme; let's just say, I have a class which defines an instance method and a protected class method. The instance method must call the class method. In order to do so, I kind of have to break the visibility rule and use the dangerous 'send' function. Something like this:
class Bang
def instance_bang
self.class.send(:class_band)
end
protected
def self.class_bang
puts "bang"
end
end
I find this awful, since the class method should be used inside the class scope, therefore should remain visible and callable within it, right? Is there an alternative way to use class methods in instance methods with needing to rely on the "send" function and therefore not break visibility?
UPDATE:
Following Sergio Tulentsev's response (thx for the correction), I'll update my concern with a code snippet that sums up my concerns of the method visibility being taken into account while still inside the scope where it has been defined.
class Bang
def instance_bang
private_bang = 1
self.private_bang(private_bang)
end
private
def private_bang(p)
puts "bang"
p
end
end
Calling Bang.new.instance_bang will raise an Exception unless you use send on that private_bang call (this time I checked it :) ).
EDIT: Answering the updated question
It is forbidden to call private methods with explicit receiver. You either have to use implicit receiver (private_bang, without self) or use send. Please see my another answer for more information.
By the way, the original question is about calling class instance methods from instance methods. Your clarification doesn't include that. But if that's still true, you have to use self.class.send or make the method public (so that you can use explicit receiver).
Let's consider a private class method (since protected class methods don't make sense).
We know it's possible for an instance to call a private method on itself, as long as it isn't using an explicit receiver (self.call_something_private). It seems you also expect that an instance can call a private class method on its own class, but that is not the case.
Let's look at a way to do this without using send.
The private and protected macros only affect instance methods of the current scope, not class methods. Here are three ways to rewrite your original code:
class Bang
def instance_bang
self.class.class_bang
end
# declare method visibility after
def self.class_bang
puts "bang"
end
private_class_method :class_bang
# inline
private_class_method def self.class_bang
puts "bang"
end
# class scope
class << self
# the private macro works here because we're inside the class scope
private
def class_bang
puts "bang"
end
end
end
So now we want to expose an interface on the class to call class_bang, but only if it's called by an instance of Bang.
class Bang
def instance_bang
self.class.invoke_class_bang(self)
end
class << self
private
def class_bang
puts "bang"
end
public
# we ask the receiver to pass itself as an argument ...
def invoke_class_bang(receiver)
# ... so that we can check whether it's
class_bang if receiver.is_a?(Bang)
end
end
end
That's not a very nice looking solution though. Here's a sneakier way:
class Bang
def initialize
def self.instance_bang() self.class.method(:class_bang).call end
end
class << self
private
def class_bang
puts "bang"
end
end
end
"The class method should be used inside the class scope, therefore should remain visible and callable within it, right?" Yes, that's correct, and that's the behavior Ruby exhibits. (As a point of clarification, instance scope is not "within" class scope. They are, appropriately, separate.)
The non-send solution is to subclass or reopen the class to add a public class method to access the protected class method.