View Source Attributes

Attributes specify the name, type and additional configuration of a simple property of a record. When using SQL data layers, for example, an attribute would correspond to a column in a database table. For information on types, see Ash.Type.

To see all of the options available when building attributes, see Ash.Resource.Dsl.attributes.attribute

If you are looking to compute values on demand, see the Calculations guide and the aggregates guide.

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

Creates a generated integer primary key. Keep in mind that not all data layers support auto incrementing ids, but for SQL data layers this is a very common practice. For those that don't, it is your own job to provide values for the primary key. We generally suggest using UUIDs over integers, as there are a lot of good reasons to not use autoincrementing integer ids.

integer_primary_key :id is equivalent to:

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