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
Related
My Rails have gotten rather rusty and I'm driving myself crazy trying to figure out something that is probably so basic I can't see the forest for the trees.
I have a form that goes to the create action of my controller. When I save I need to also update some items from another table. I want to wrap it all in a transaction. I thought the preference was to put the transaction in the model. When I do that and try to call the create action it errors out telling me that there is no method for that class.
equip_swaps_controller.rb
def create
respond_to do |format|
#equip_swap = EquipSwap.new(equip_swap_params)
if #equip_swap.trans_equip_and_save
format.html { redirect_to #equip_swap, notice: 'Equipment transfer was successfully created.' }
else
format.html { render action: 'failure' }
end
end
end
Model equip_swap.rb
def self.trans_equip_and_save
EquipSwap.transaction do
Tool.transfer_equipment(self.to_vehicle, self.items_moved)
self.save
end
end
Tool model with needed method
def transfer_equipment(location,ids)
ids.each do |id|
Tool.find(id).update(location: location)
end
end
I thought that calling the class method would allow it to execute that method on my instance of the EquipSwap instance #equip_swap. When I try to submit the form and create the new record it tells me that there is no trans_equip_and_save method for Class..... There is something obvious that I'm missing. Help!
Method start with self its call class method and and without self its call instance method, let me give example
Class method
def self.class_method
# do some stuff
end
Instance method
def instance_method
# do some stuff
en
Call class method using
ModelName.class_method
Call instance method using
#instance_variable.instance_method
In your code change your method to instance method
def trans_equip_and_save
EquipSwap.transaction do
Tool.transfer_equipment(self.to_vehicle, self.items_moved)
self.save
end
end
And now call this method using instance variable #equip_swap.trans_equip_and_save
Edit:
If you are calling transfer_equipment using model name then add self before method name, I mean make it class method like following
def self.transfer_equipment(location,ids)
ids.each do |id|
Tool.find(id).update(location: location)
end
end
You have two things to notice here,
First of all there are two different methods, class methods and instance methods.
Class methods: Class methods are defined directly on a class and they are defined using def self.method.
Usage: Class.method
Instance methods: Instance methods are defined on an object of a class and they are defined without self.
Usage: object = Class.new(), def method ==> object.method
So, in your case, there will be two changes,
1) you called, #equip_swap.trans_equip_and_save.
Since, #equip_swap is an object, according to second point you shold have an Since, #equip_swap is an object, according to second point you shold have an instance method without self..
def trans_equip_and_save
EquipSwap.transaction do
Tool.transfer_equipment(self.to_vehicle, self.items_moved)
self.save
end
end
2) Tool.transfer_equipment, this is called with class name. So, according to first point it should be called with self.
def self.transfer_equipment(location,ids)
ids.each do |id|
Tool.find(id).update(location: location)
end
end
I have an instance method that has logic I want to use in a query. My attempts have not worked. I'd rather not duplicate the logic inside is_thing when building my where clause.
class Foo < ActiveRecord::Base
def is_thing?
#... some logic
end
end
I tried
Foo.where(is_thing?)
and got
NoMethodError: undefined method `is_thing?' for main:Object
The Approach I would recommend
I do believe that method is not good practice (to chain a where query). It will only add unnecessary complexity.
The better approach is using scope
scope :is_thing?, -> { where(thing: true) }
and call it
Foo.is_thing?.where()
The Why
The reason it is returned
NoMethodError: undefined method `is_thing?' for main:Object
Is because is_thing? is instance variable of Foo
Instance variable can be called on an instance of the class. And not availabe on main object.
You, however could do
Foo.where(Foo.new.is_thing?)
It is posible to use that if you convert is_thing? to class method. e.g
def self.is_thing?
# code
end
and use it this way
Foo.where(Foo.is_thing?)
try this:
class Foo < ActiveRecord::Base
def is_thing?
#... some logic
end
def things
Foo.where('thing_check = ?', self.is_thing?)
end
end
create another instance method to wrap your where query. Then access it as Foo.last.things
# 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 studied major difference between Ruby class ,instance method and the major difference I found is we don't need to create instance of that class we can directly call that method on class name directly.
class Notifier
def reminder_to_unconfirmed_user(user)
headers['X-SMTPAPI'] = '{"category": "confirmation_reminder"}'
#user = user
mail(:to => #user["email"], :subject => "confirmation instructions reminder")
end
end
So,here I defined instance method reminder_to_unconfirmed_user in my Notifier class to send email to unconfirmed users, and when I run Notifier.reminder_to_unconfirmed_user(User.last) it get called provided it's a instance method not a class method.
To define a class method, use the self keyword in the method's definition (or the class' name):
class Notifier
def self.this_is_a_class_method
end
def Notifier.this_a_class_method_too
end
def this_is_an_instance_method
end
end
In your case, reminder_to_unconfirmed_user should be defined as a class method:
class Notifier
def self.reminder_to_unconfirmed_user(user)
# ...
end
end
Then you can use it like this:
Notifier.reminder_to_unconfirmed_user(User.last)
I had the same question the OP did and after digging around I finally figured it out! The other answers just addressed when to use instance vs class methods in Ruby however Rails does some sneaky stuff behind the scences. The question wasn't when to use class vs instance methods but instead how come Rails allows you to call an instance method as if it's a class method as shown by his mailer example above. It's due to: AbstractController::Base and can be seen here: AbstractController::Base
Basically, in all controllers (whether they be your mailer or a standard controller), all defined methods are intercepted by "method_missing" and then returns an instance of that class! The defined methods are then also converted to public instance methods. Thus, because you never instantiate these classes (for example you never do Mailer.new.some_method) Rails automagically calls method_missing and returns an instance of that Mailer which then takes advantage of all the methods defined within that class.
In your case it must be :
class Notifier
def self.reminder_to_unconfirmed_user(user)
headers['X-SMTPAPI'] = '{"category": "confirmation_reminder"}'
#user = user
mail(:to => #user["email"], :subject => "confirmation instructions reminder")
end
end
As their name suggests:
Instance methods on a model should be used for logic/operations that relate to a specific instance of a model (the one on which the method is called.)
Class methods are for things which don't operate on an individual instance of a model or for cases where you don't have the instance available to you. Like in some cases you do want to apply changes on few group of objects.
If you want to update all users on a specific condition, Then you should go for class method.
They do have different way of calling :
class Test
def self.hi
puts 'class method'
end
def hello
puts 'instance method'
end
end
Foo.hi # => "class method"
Foo.hello # => NoMethodError: undefined method ‘hello’ for Test:Class
Foo.new.hello # => instance method
Foo.new.hi # => NoMethodError: undefined method ‘hi’ for #<Test:0x1e871>
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.