livebook/ash_tutorial/querying.livemd

# Ash: 3 - Querying

```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)
```

## But First, Data Persistence

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So far we have just created changesets, but we have not actually created any instances of a resource, also known as records.  Before we can play around with querying, we need to add a data layer.  It is much more common to use [Postgres](https://github.com/ash-project/ash_postgres) in production, but we will use [ETS data layer](https://hexdocs.pm/ash/dsl-ash-datalayer-ets.html#ets) for the remainder of this tutorial to keep dependencies to a minimum.

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```elixir
 use Ash.Resource,
      domain: YourDomain,
      data_layer: Ash.DataLayer.Ets
```

## In this tutorial you will do basic Query and CRUD operations

But first you need to enable all basic **CRUD** operations.

Do this by adding default `:read` and `:destroy` actions, as well as `:create` and `:update` actions that accept `[:name]`.

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  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

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

    actions do
      defaults [:read, :destroy]

      create :create do
        accept [:name]
      end

      update :update do
        accept [:name]
      end
    end

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

  defmodule Tutorial do
    use Ash.Domain

    resources do
      resource Tutorial.Profile
    end
  end
  ```

  </div>
</details>

### Enter your solution

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

  actions do
    # <--- Create your actions here
  end

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

defmodule Tutorial do
  use Ash.Domain

  resources do
    resource Tutorial.Profile
  end
end
```

## Creating

Add 2 Profiles to the database.

* One with the name "Joe Armstrong"
* One with your name

You can create a `Profile` by:

* Creating a Changeset with `Ash.Changeset.for_create(Tutorial.Profile, :create, %{name: "Your Name"})`,
* Then giving the changeset to `Ash.create!()`.

*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.Profile
  |> Ash.Changeset.for_create(:create, %{name: "The Name"})
  |> Ash.create!()
  ```

  </div>
</details>

**Enter your solution**

```elixir

```

## Reading

Now, read all the generated Profiles.

Call `Ash.read!/1` with the `Tutorial.Profile` module.

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  ```elixir
  Tutorial.Profile
  |> Ash.read!()
  ```

  </div>
</details>

**Enter your solution**

```elixir

```

Now fetch the "Joe Armstrong" Profile.

You can achieve this by introducing a filter.

First you'll need to `require Ash.Query`

Then call `Ash.Query.filter(name == "Joe Armstrong")` with the `Tutorial.Profile`.

Put the result into the `joe` variable. `Ash.read!/1` returns a list, so make sure to extract the single returned value out of that list.

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  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  require Ash.Query

  [joe] =
    Tutorial.Profile
    |> Ash.Query.filter(name == "Joe Armstrong")
    |> Ash.read!()
  ```

  </div>
</details>

**Enter your solution**

```elixir

```

You'll use the `joe` variable in the next sections.

## Updating

Now change `Joe Armstrong`'s name to `Neil Armstrong`.

You can do this by providing the `Ash.Changeset.for_update/3` with:

* the resource you want to change, in this case `joe`
* the `:update` atom
* a map of the values you want to change, in this case `%{name: "Neil Armstrong"}`

Then apply the changeset by calling `Ash.update!/1` with the changeset.

*Hint: Using a pipeline might be a good idea.*

<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
  joe
  |> Ash.Changeset.for_update(:update, %{name: "Neil Armstrong"})
  |> Ash.update!()
  ```

  </div>
</details>

**Enter your solution**

```elixir

```

## Destroying

Finally, remove `joe` from the database.

Do this using the `Ash.destroy!/1` function.

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  <summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
  <div class="p-4">

  ```elixir
  Ash.destroy!(joe)
  ```

  </div>
</details>

**Enter your solution**

```elixir

```

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