How ActiveRecord Serializes a Ruby Object

2013.02.25

Let’s assume we have a table named posts. The table has only one column, title, which will store just that: a post’s title. For this hypothetical exercise, we’ll be using ActiveRecord as our ORM.

Let’s also assume that we’re using the handy Faker::Lorem.words() function to generate some test data. We’ll pass the number three to the words function to get what will stand in as a passable title for testing purposes. Finally, let’s assume that we forget that words returns an array of words, rather than a string of three words.

What happens when we do the following?

post = Post.create(:title => Faker::Loream.words(3))

Will ActiveRecord throw an error about storing a Ruby object in the database? Or, will it do something else?

This past week, I found myself overlooking this detail and getting some strange behavior, which upon closer inspection makes sense. When I retrieved the test post’s title from the database, look what came back:

  --- -lorem -ipsum -dolor

It’s Yaml! Instead of complaining about receiving a non-string, ActiveRecord will serialize a Ruby object using Yaml. What strange and unexpected behavior.