livebook/ash_tutorial/code_interfaces.livemd

# Ash: 7 - Code Interfaces

```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)
```

## Code Interfaces

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### In this tutorial you will add a Code Interface

In previous tutorials you always used `Changesets` directly to CRUD on resources.
While this is a perfectly valid way of handling CRUD operations, Ash provides [Code Interfaces](https://hexdocs.pm/ash/code-interfaces.html) to make this more ergonomic for you.
The code interface can be defined on the resources *or* the domain. In this example, we will define it on the domain.

You will add 3 code interfaces for:

* Creating a representative
* Opening a ticket
* Assigning a representative

For each resource you want to add a code interface to, inside that resource definition on the domain, you will place "definitions".
For example:

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

```elixir
resource MyApp.Tweet do
  define :create_tweet, args: [:content]
end
```

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

Then add the 3 interfaces by defining the following inside the `Ticket` resource's block:

* `define :assign_ticket, args: [:representative_id], action: :assign`
* `define :open_ticket, args: [:subject, :description], action: :open`

And the following inside the `Representative` resource's block.

* `define :create_representative, args: [:name], action: :create`

<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
  resource Tutorial.Support.Ticket do
    define :assign_ticket, args: [:representative_id], action: :assign
    define :open_ticket, args: [:subject, :description], action: :open
  end

  resource Tutorial.Support.Representative do
    define :create_representative, args: [:name], action: :create
  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 :open do
      accept [:subject, :description]
    end

    update :close do
      change set_attribute(:status, :closed)
    end

    update :assign do
      accept [:representative_id]
    end
  end

  attributes do
    uuid_primary_key :id
    attribute :subject, :string, allow_nil?: false
    attribute :description, :string, allow_nil?: true

    attribute :status, :atom do
      constraints one_of: [:open, :closed]
      default :open
      allow_nil? false
    end

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  relationships do
    belongs_to :representative, Tutorial.Support.Representative
  end
end

defmodule Tutorial.Support.Representative do
  use Ash.Resource,
    domain: Tutorial.Support,
    data_layer: Ash.DataLayer.Ets

  actions do
    defaults [:read]

    create :create do
      accept [:name]
    end
  end

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end
end

defmodule Tutorial.Support do
  use Ash.Domain

  resources do
    resource Tutorial.Support.Ticket do
      # <-- Add ticket code interface here
    end

    resource Tutorial.Support.Representative do
      # <-- Add representative code interface here
    end
  end
end
```

## Using the Code Interfaces

Create a Representative, but instead of using a changeset, use the code interface you created.

You can use a code interface by calling `Tutorial.Support.create_representative!/1` with the desired name.

Set the name to `Joe Armstrong` and store it in a `joe` variable.

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  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
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  ```elixir
  joe = Tutorial.Support.create_representative!("Joe Armstrong")
  ```

  </div>
</details>

```elixir

```

Create a Ticket with the created code interface.

Call `Tutorial.Support.open_ticket!/2` with a `subject` and `description` and store the result in a `ticket` variable.

<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
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  ```elixir
  ticket = Tutorial.Support.open_ticket!("I can't find my hand!", "I think someone stole it.")
  ```

  </div>
</details>

```elixir

```

Assign the Representative `joe` to the Ticket using the code Interface.

Use `Tutorial.Support.assign_ticket!/2`.

<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.assign_ticket!(ticket, joe.id)
  ```

  </div>
</details>

```elixir

```

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<a class="flex ml-2" style="color: #61758a;" href="relationships.livemd">Managing Relationships</a>
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