Five Practices for Robust Ruby on Rails Applications

Whenever I come across a rails application with inconsistent data or bugs that are hard to nail down I tell myself: “They (the developers) were just a couple of keystokes away from preventing those issues from happening”.

At Brewhouse, we follow five simple practices to make our Rails applications robust. It all comes down to failing early, loudly and often. We ensure that data is valid and applications behave properly by catching issues early on.

Use Hash#fetch to catch malformed hash

unexpected method 'upcase' for nil… Whenever you expect a Hash to contain a key, prefer fetch() over []. fetch() will raise an error when the key is missing so you won’t pass nil values around and see unrelated errors happening down the line.

case ... else raise to catch invalid data

Always add an else raise ... clause to your case statements. You want to know when you’ve received an unexpected value rather than ignoring it and moving on.

Use ActiveRecord ! methods to fail loudly

Data is often being seen as the most valuable asset in a company. Failing silently to persist data can have a huge impact then. Whenever you’re not expecting an operation to fail, use the “bang” version of create!, update! and destroy! that raise exceptions on failure. This extra key stroke will save you from dealing with inconsistent data.

Used in test code, it ensures that the setup doesn’t fail silently… there is nothing worse than a test that passes because the setup was incorrect.

Also, always wrap multiple calls into an SQL transaction to prevent your data from getting into an in-between state.

Add ActiveRecord validations to perform live checks

Pairing ActiveRecord validations with the use of ‘bang methods’ is a great way to ensure you persist valid data. For example:

class Post < ActiveRecord::Model
  validates :author, :blog, presence: true
  validates :published_by, presence: true, if: :published?
  validates :comment_count, numericality: { greater_or_equal_to: 0 }
  # ...
end

Use database constraints to ensure data consistency

Your database is your best friend when it comes to ensuring data is present, not duplicated and that orphans are not left in the database.

null: false

Given the fact that the large majority of columns are required in a database, you should define columns with null: false by default.

index ... unique: true

Did you know that rails has_one does not prevent duplicate associations from being created?

class Account
  has_one :account_settings
end

account = Account.create!
account.create_account_settings!
account.create_account_settings!
account.create_account_settings!

account.account_settings
 # => one of the three account settings you've created... -_-

The best way to prevent this from making data inconsistent is to add a unique index.

add_index :account_settings, :account_id, unique: true

The database will throw an error if you attempt to persist a duplicate record.

foreign_key

You don’t want orphan records in your database, do you?

Foreign keys help such things from happening. I’d recommend using the ruby gem schema_auto_foreign_keys to automatically add foreign keys on your behalf.

A few extra keystrokes goes a long way

A few extra keystrokes here and there can save you from hours of debugging or recovering from inconsistent data. Use !, raise, validate and database constraints. Your coworkers and future-self will thank you.

As always, feedback is greatly appreciated. I’d be happy to hear of any other practices I didn’t cover here.