mirror of
https://github.com/ash-project/ash.git
synced 2024-09-20 13:33:20 +12:00
95 lines
2.6 KiB
Markdown
95 lines
2.6 KiB
Markdown
# 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:
|
|
|
|
```elixir
|
|
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:
|
|
|
|
```elixir
|
|
attribute :inserted_at, :utc_datetime_usec do
|
|
writable? false
|
|
private? true
|
|
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:
|
|
|
|
```elixir
|
|
attribute :updated_at, :utc_datetime_usec do
|
|
writable? false
|
|
private? true
|
|
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:
|
|
|
|
```elixir
|
|
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](https://www.clever-cloud.com/blog/engineering/2015/05/20/why-auto-increment-is-a-terrible-idea/). 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:
|
|
|
|
```elixir
|
|
attribute :id, :integer do
|
|
writable? false
|
|
generated? true
|
|
primary_key? true
|
|
allow_nil? false
|
|
end
|
|
```
|