In most Ruby on Rails models I’ve seen dependent: :destroy being used to handle child objects when a parent object is destroyed. I don’t know why it took me this long to learn that there is also a :nullify option. Using dependent: :nullify is handy for situations where keeping associated objects after destroying the parent object is important (data retention purposes, etc).

For example, let’s say we had a category model and a transaction model defined like so:

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class Category < ApplicationRecord
  has_many :transactions, dependent: :nullify
end

class Transaction < ApplicationRecord
  belongs_to :category
end

With this setup, if a category is deleted, and it has transactions associated, the category_id field on each transaction is set to null. The category is deleted but the transactions remain. A new category can then be set for each transaction, or the association can be left as null.

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