ActiveRecord: Doesnt call after_initialize when method name is passed as a symbol

问题

I noticed that Rails doesn't trigger after_initialize callback when the callback symbol is passed as input.

The code below doesn't work.

class User < ActiveRecord::Base
  after_initialize :init_data

  def init_data
    puts "In init_data"
  end

end

The code below works.

class User < ActiveRecord::Base

  def after_initialize 
    init_data
  end

  def init_data
    puts "In init_data"
  end
end

Can somebody explain this behavior?

Note 1

The ActiveRecord documentation says the following about after_initialize:

Unlike all the other callbacks, after_find and after_initialize will 
only be run if an explicit implementation is defined (def after_find). 
In that case, all of the callback types will be called.

Though it is stated that after_initialize requires explicit implementation, I find the second sentence in the above paragraph ambiguous, i.e. In that case, all of the callback types will be called. What is all of the call back types?

The code sample in the documentation has an example that doesn't use explicit implementation:

after_initialize EncryptionWrapper.new

回答1:

According to the documentation, you cannot use the macro-style class methods for the after_initialize or after_find callbacks:

The after_initialize and after_find callbacks are a bit different from the others. They have no before_* counterparts, and the only way to register them is by defining them as regular methods. If you try to register after_initialize or after_find using macro-style class methods, they will just be ignored. This behaviour is due to performance reasons, since after_initialize and after_find will both be called for each record found in the database, significantly slowing down the queries.

In short, you have to define an after_initialize instance method:

class User < ActiveRecord::Base

  def after_initialize
    do_stuff
  end

end

回答2:

I'm pretty sure that methods invoked by symbol need to be protected or private.

Edit: Yep, here's the Rails 3 documentation:

The method reference callbacks work by specifying a protected or private method available in the object

来源：https://stackoverflow.com/questions/3826153/activerecord-doesnt-call-after-initialize-when-method-name-is-passed-as-a-symbo

标签

ruby-on-rails

activerecord