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ActiveRecord is still magical

Neeraj Singh

Abstract

ActiveRecord is complex code and because of complexity it has edge cases. In fact lots of edge cases. We will take a look at a number of ActiveRecord features to see how it works and how to deal with some of the edge cases.

We will see how default_scope works. And why method "unscoped" removes default_scope from models but not from associations.

Do you know the difference between CollectionProxy and Relation ? Do you know why in a has_many through case "@physician.patients.create!" would work but "@physician.patients.where(active: true).create! would silently fail without creating the association record ?

We will discuss why while patching Active Record you should run your tests against all three databases.

Guess which of these two obey :destroy option: @customer.orders.delete(@order) or @customer.orders.destroy(@order) .

In Rails 3 when where conditions are merged then the last where condition wins. In Rails 4 all the where conditions are 'And'ed. But not defautl_scope. We will see how and why.

Will also discuss implementation detail of features like inverse_of, autosave and callbacks.

Additional Notes

Last few months I have been fixing Active Record issues and in the process have learned a lot about inner workings of Active Record. In this talk I will share some of the things I learned.

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