livebook/ash_tutorial/attributes.livemd

# Ash: 4 - Attributes

```elixir
Application.put_env(:ash, :validate_domain_resource_inclusion?, false)
Application.put_env(:ash, :validate_domain_config_inclusion?, false)
Mix.install([{:ash, "~> 3.0"}], consolidate_protocols: false)
```

## Attributes

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### In this tutorial you will add and configure Attributes to a Ticket resource

The Ticket resource will represent a helpdesk ticket.

It will have 3 main attributes.

* A `subject` or title
* A `description`
* A `status` which can be either `:open` or `:closed`

It will also have 2 attributes for keeping track of when the ticket was *created*, and when it was *last updated*.

#### Subject

You need to make sure the `subject` is always set, it's not possible to create a ticket without a subject. You can do this by setting `allow_nil?` to `false`. Like so: `attribute :subject, :string, allow_nil?: false`

#### Description

The `:description` is simple, it's a `:string` and it is allowed to be empty.

#### Status

`:status` is more complicated.

* It is of the type `:atom`
* It can only be the value `:open` or `:closed`
* By default it is `:open`
* And it can't be `nil`

Attributes are set in a `do end` block like so:

<!-- livebook:{"force_markdown":true} -->

```elixir
attribute :status, :atom do

  # ...

  allow_nil? false
end
```

To set a constraint of values, you can use the `constraints` option, like so:

`constraints [one_of: [:open, :closed]]`

To set the default value, you use `default :open`.

#### Keeping track of Created and Updated

Ash provides [create_timestamp](https://hexdocs.pm/ash/dsl-ash-resource.html#attributes-create_timestamp) and [update_timestamp](https://hexdocs.pm/ash/dsl-ash-resource.html#attributes-update_timestamp) to keep track of when the Resource was first created, and when it was last updated.

Add the following to the attributes block:

<!-- livebook:{"force_markdown":true} -->

```elixir
create_timestamp :created_at
update_timestamp :updated_at
```

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  defmodule Tutorial.Support.Ticket do
    use Ash.Resource,
      domain: Tutorial.Support,
      data_layer: Ash.DataLayer.Ets

    actions do
      defaults [:read]

      create :create do
        accept [:subject, :description, :status]
      end
    end

    attributes do
      uuid_primary_key :id

      attribute :subject, :string, allow_nil?: false
      attribute :description, :string

      # status is either `open` or `closed`.
      attribute :status, :atom do
        # Constraints allow you to provide extra rules for the value.
        # The available constraints depend on the type
        # See the documentation for each type to know what constraints are available
        # Since atoms are generally only used when we know all of the values
        # it provides a `one_of` constraint, that only allows those values
        constraints [one_of: [:open, :closed]]

        default :open
        allow_nil? false
      end

      create_timestamp :created_at
      update_timestamp :updated_at
    end
  end

  defmodule Tutorial.Support do
    use Ash.Domain

    resources do
      resource Tutorial.Support.Ticket
    end
  end
  ```

  </div>
</details>

### Enter your solution

```elixir
defmodule Tutorial.Support.Ticket do
  use Ash.Resource,
    domain: Tutorial.Support,
    data_layer: Ash.DataLayer.Ets

  actions do
    defaults [:read]

    create :create do
      accept [:subject, :description, :status]
    end
  end

  attributes do
    uuid_primary_key :id

    # Add the attributes here -->
    # - Subject
    # - Description
    # - Status
    # - Create Timestamp
    # - Update Timestamp
  end
end

defmodule Tutorial.Support do
  use Ash.Domain

  resources do
    resource Tutorial.Support.Ticket
  end
end
```

## Creating a Ticket

Create a `Ticket` without any attributes.

Remember, when creating a resource use a changeset (`Ash.Changeset.for_create/3`), which gets passed to `Ash.create!/1`.

The output should look something like this:

```
** (Ash.Error.Invalid) Input Invalid

* attribute subject is required
```

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Tutorial.Support.Ticket
  |> Ash.Changeset.for_create(:create, %{})
  |> Ash.create!()
  ```

  </div>
</details>

```elixir

```

Now create a Ticket with a `subject`

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Tutorial.Support.Ticket
  |> Ash.Changeset.for_create(:create, %{subject: "This is the subject"})
  |> Ash.create!()
  ```

  </div>
</details>

```elixir

```

Now create a ticket with the `status` set to `:closed`

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Tutorial.Support.Ticket
  |> Ash.Changeset.for_create(:create, %{subject: "This is the subject", status: :closed})
  |> Ash.create!()
  ```

  </div>
</details>

```elixir

```

Now try creating a ticket with the status set to `:pending`. This should give an error because `:pending` is not a valid `status`.

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Tutorial.Support.Ticket
  |> Ash.Changeset.for_create(:create, %{subject: "This is the subject", status: :pending})
  |> Ash.create!()
  ```

  </div>
</details>

```elixir

```

## Latest created Ticket

Since you added a creation date, you can now query on the latest created ticket.

First, sort using the `Ash.Query.sort/2` function by `Ash.Query.sort(created_at: :desc)`

Then limit the amount of records with the `Ash.Query.limit/2` function by doing `Ash.Query.limit(1)`

Finally call `Ash.read_one!()` on the query.

*Hint: Use a pipeline*

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Tutorial.Support.Ticket
  |> Ash.Query.sort(created_at: :desc)
  |> Ash.Query.limit(1)
  |> Ash.read_one!()
  ```

  </div>
</details>

```elixir

```

<div class="flex items-center w-full flex-start justify-between rounded-xl p-4" style="background-color: #f0f5f9; color: #61758a;">
<div class="flex">
<i class="ri-arrow-left-fill"></i>
<a class="flex ml-2" style="color: #61758a;" href="querying.livemd">Querying</a>
</div>
<div class="flex">
<i class="ri-home-fill"></i>
<a class="flex ml-2" style="color: #61758a;" href="overview.livemd">Home</a>
</div>
<div class="flex">
<a class="flex mr-2" style="color: #61758a;" href="customizing_actions.livemd">Customizing Actions</a>
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