Module: Mcmire::AfterTimestamps

Defined in:
lib/mcmire/after_timestamps.rb

Overview

You probably know that every time a record is created, its created_at field is automatically filled in. And every time a record is updated, its updated_at field is filled in. This “magic” happens because of ActiveRecord’s Timestamp module, which is mixed in when ActiveRecord::Base is require()‘d.

Unfortunately, if you want to adjust these times for any reason before the record is actually saved to the database, there isn’t a built-in way to do this. So, what we have to end up doing is inserting another method into the ActiveRecord callback chain. However, doing so can be kind of tricky if you don’t know what’s going on behind the scenes. This is because ActiveRecord starts out with a set of standard methods in AR::Base and then several modules are mixed in that override some of those methods.

The methods that we are concerned about are the ones that are called when you say ‘some_record.save`:

         save
          |
   create_or_update
    /           \
create         update

The modules which are mixed into AR::Base that we are concerned about are AR::Timestamp and AR::Callbacks. Both use alias_method_chain to override the methods, so you will see that below. Anyway, when AR::Timestamp is mixed in this is what the call tree like:

                            save
                             |
                      create_or_update
              ......./                \.......
             /                                \
 create(_with_timestamps)         update(_with_timestamps)
            |                                 | 
create_without_timestamps         update_without_timestamps

(The parentheses are there to indicate the effects of alias_method_chain.)

And when AR::Callbacks is mixed in, the tree changes again:

                                save
                                 |
                  create_or_update(_with_callbacks)
                                 |
                           before_save
                                 |
                 create_or_update_without_callbacks
             ............/   ^   |   ^    \..........
            v                |   |   |               v
 create(_with_callbacks)     |   |   |     update(_with_callbacks)
           |                 |   |   |                |
     before_create           |   |   |          before_update
           |                 |   |   |                |
create_without_callbacks     |   |   |    update_without_callbacks
           |                 |   |   |                |
create_without_timestamps   /    |    \   update_without_timestamps
           |               /     |     \              |
      after_create .......´      |      '....... after_update
                                 |
                                 v
                             after_save

As you can see, when the before_save callback is fired, the timestamps haven’t been set yet. Even at before_create/before_update, the timestamps still haven’t been set yet. Of course, by the time after_create/after_update, it’s too late to adjust the timestamps, since the record has already been saved.

That’s why we need to insert a custom callback in the chain. We do this by simply alias_method_chain()‘ing create_without_timestamps and update_without_timestamps to do what we want.

Constant Summary collapse

VERSION = 
"0.2.0"

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.included(klass) ⇒ Object 



77
78
79
80
81
82
83
 
# File 'lib/mcmire/after_timestamps.rb', line 77

def self.included(klass)
  klass.class_eval do
    alias_method_chain :create_without_timestamps, :after_timestamps
    alias_method_chain :update_without_timestamps, :after_timestamps
    define_callbacks :after_timestamps_on_create, :after_timestamps_on_update
  end
end

Instance Method Details

#after_timestamps_on_create ⇒ Object 



85
 
# File 'lib/mcmire/after_timestamps.rb', line 85

def after_timestamps_on_create() end

#after_timestamps_on_update ⇒ Object 



86
 
# File 'lib/mcmire/after_timestamps.rb', line 86

def after_timestamps_on_update() end