til/ruby/specify-default-for-data-definition.md

Specify Default For Data Definition

Here is what a Data definition for the concept of a Permission might look like:

Permission = Data.define(:id, :name, :description, :enabled)

perm1 = Permission.new(
  id: 123,
  name: :can_edit,
  description: "User is allowed to edit.",
  enabled: true
)

However, as we're creating various Permission entities, we may find that the vast majority of them are enabled by default and so we'd like to apply true as a default value.

We cannot do this directly in the Data definition, but we can open a block to override the initialize method.

Permission = Data.define(:id, :name, :description, :enabled) do
  def initialize(:id, :name, :description, enabled: true)
    super
  end
end

perm1 = Permission.new(
  id: 123,
  name: :can_edit,
  description: "User is allowed to edit."
)

perm1.enabled #=> true

Now we're able to create a Permission without specifying the enabled attribute and it takes on the default of true.

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