Keep Defaults

Prevent ActiveRecord attributes for not null columns with default values from being set to nil.

Why is this necessary? Take this example:

class OrderItem < ApplicationRecord
  # Has column: total numeric(11,2) not null default 0
  # Validation etc...
end

class Order < ApplicationRecord
  # Has columns: total and taxes, both numeric(11,2) not null default 0
  # Validation etc...

  has_many :order_items

  def total
    order_items.sum(&:total) + taxes
  end
end

The columns have a default value of 0, but the attributes can still be set to nil. This can make for code that is far from bulletproof:

o = Order.new
o.total  # 0
o.taxes = nil
o.total  # 💥 TypeError: nil can't be coerced into Fixnum

To fix you can do something like:

class Order < ApplicationRecord
  def total
    order_items.sum(&:total) + taxes.to_f
  end
end

But OrderItem#total can be set to nil too. You can do:

class OrderItem < ApplicationRecord
  def total
    super || 0
  end
end

But what about the other contexts in which these can be called or the other attributes you may have? This can get tedious.

With Keep Defaults:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  # Must come after setting abstract_class
  include KeepDefaults
end

o = Order.new
o.total  # 0
o.taxes = nil
o.total  # 0
o.taxes  # 0

Now if an attribute is set to nil it will retain —or be returned to— its default value instead.

Installation

Add this line to your application's Gemfile:

gem "keep_defaults"

Or

gem install keep_defaults

Usage

To use everywhere add to ApplicationRecord:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  # Must come after setting abstract_class
  include KeepDefaults
end

To use for a specific class add it directly to that class:

class Order < ApplicationRecord
  include KeepDefaults
end

If your class sets its table via table_name then include KeepDefaults must come after that.

Using With an Existing Column

To ensure that an attribute always returns its default value you must make sure its DB column does not allow null and has a default.

For example, given the column orders.taxes that does not meet these requirements, you can add a migration containing the following:

def change
  change_column :orders, :taxes, :integer, :null => false, :default => 0
end

Known Issues

Classes That Explicitly Set table_name and Have an Ancestor Class That includes KeepDefaults

In this case include KeepDefaults must be taken out of the ancestor classes in added to all the subclasses.

License

The gem is available as open source under the terms of the MIT License.