ash/documentation/topics/attributes.md

Attributes

Attributes specify the name, type and properties of a piece of information in a resource.

Ways of writing attributes

There are two ways to write an attribute:

attribute :name, :string, allow_nil?: false

# or ...
attribute :name, :string do
  allow_nil? false
end

Both ways will work. Though when you're using many options the latter is preferred. This is also true of any other keyword in the Ash DSL, so you can build a flexible yet concise domain model.

For more information on attribute types including composite types and defining your own custom type see Ash.Type

You can find a comprehensive of attribute options with detailed descriptions on the d:Ash.Resource.Dsl.attributes page.

Special attributes

In Ash there are 4 special attributes these are:

• create_timestamp
• update_timestamp
• integer_primary_key
• uuid_primary_key

These are really just shorthand for an attribute with specific options set. They're outlined below.

create_timestamp

You may recognise this if you have used Ecto before. This attribute will record the time at which each row is created, by default it uses DateTime.utc_now/1.

create_timestamp :inserted_at is equivalent to an attribute with these options:

attribute :inserted_at, :utc_datetime_usec do
  writable? false
  default &DateTime.utc_now/0
  match_other_defaults? true
  allow_nil? false
end

update_timestamp

This is also similar in Ecto. This attribute records the last time a row was updated, also using DateTime.utc_now/1 by default.

update_timestamp :updated_at is equivalent to:

attribute :updated_at, :utc_datetime_usec do
  writable? false
  default &DateTime.utc_now/0
  update_default &DateTime.utc_now/0
  match_other_defaults? true
  allow_nil? false
end

uuid_primary_key

This attribute is used in almost every resource. It generates a UUID every time a new record is made. uuid_primary_key :id is equivalent to:

attribute :id, :uuid do
  writable? false
  default &Ash.UUID.generate/0
  primary_key? true
  allow_nil? false
end

integer_primary_key

Don't use this attribute unless absolutely necessary, there are a lot of good reasons to not use autoincrementing integer ids. If you do, please make sure these resource are only accessed internally and aren't exposed via a public API.

integer_primary_key :id is equivalent to:

attribute :id, :integer do
  writable? false
  generated? true
  primary_key? true
  allow_nil? false
end