form.html.eex

<%= form_for @changeset, @action, fn f -> %>
  <%= if @changeset.action do %>
    <p> Something is broken. Check the following: </p>
    <ul>
      <%= for {attr, message} <- f.errors do %>
        <li>
          <%= humanize(attr) %>
          &nbsp;
          <%= message %>
        </li>
      <% end %>
    </ul>
  <% end %>

  <%= label f, :name %>
  <%= text_input f, :name %>

  <%= label f, :description %>
  <%= text_input f, :description %>

  <%= label f, :seo_slug %>
  <%= text_input f, :seo_slug %>

  <%= inputs_for f, :variants, fn v -> %>
    <%= label v, :price %>
    <%= text_input v, :price %>

    <%= label v, :sale_price %>
    <%= text_input v, :sale_price %>

    <%= label v, :available %>
    <%= text_input v, :available %>

    <%= label v, :sku %>
    <%= text_input v, :sku %>

    <%= if v.model.id do %>
      <%= label v, :delete, "Delete?" %>
      <%= checkbox v, :delete %>
    <% end %>

    <%= inputs_for v, :variant_images, [multipart: true], fn i -> %>
      <%= label i, :image %>
      <%= file_input i, :image %>
    <% end %>
  <% end %>

  <%= submit "Submit" %>
<% end %>

params

[debug] Processing by Dumaine.ProductController.create/2
  Parameters: %{"_csrf_token" => "Oz4ZSmsZJjEUBhtkCzQGGBQEICF7NgAAvhIrYzVGYahVfN0+bTdXCg==", "_utf8" => "✓", "product" => %{"description" => "All natural!", "name" => "Belt", "seo_slug" => "belt", "variants" => %{"0" => %{"available" => "5", "price" => "123", "sale_price" => "123", "sku" => "abc-123", "variant_images" => %{"0" => %{"image" => "approved.jpg"}}}, "1" => %{"available" => "2", "price" => "44", "sale_price" => "44", "sku" => "abc-111", "variant_images" => %{"0" => %{"image" => "dangerous.jpeg"}}}}}}
  Pipelines: [:browser]
[debug] BEGIN [] OK query=0.3ms
[debug] INSERT INTO "products" ("description", "inserted_at", "name", "seo_slug", "updated_at") VALUES ($1, $2, $3, $4, $5) RETURNING "id" ["All natural!", {{2015, 12, 10}, {5, 24, 34, 0}}, "Belt", "belt", {{2015, 12, 10}, {5, 24, 34, 0}}] OK query=0.4ms
[debug] INSERT INTO "variants" ("available", "inserted_at", "price", "product_id", "sale_price", "sku", "updated_at") VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING "id" [5, {{2015, 12, 10}, {5, 24, 34, 0}}, 123, 15, 123, "abc-123", {{2015, 12, 10}, {5, 24, 34, 0}}] OK query=0.3ms
[debug] INSERT INTO "variants" ("available", "inserted_at", "price", "product_id", "sale_price", "sku", "updated_at") VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING "id" [2, {{2015, 12, 10}, {5, 24, 34, 0}}, 44, 15, 44, "abc-111", {{2015, 12, 10}, {5, 24, 34, 0}}] OK query=0.4ms
[debug] COMMIT [] OK query=6.1ms

product.ex

defmodule Dumaine.Product do
  use Dumaine.Web, :model

  schema "products" do
    field :name, :string
    field :description, :string
    field :seo_slug, :string
    has_many :variants, Dumaine.Variant, on_delete: :fetch_and_delete

    timestamps
  end

  @required_fields ~w(name description seo_slug variants)
  @optional_fields ~w()

  @doc """
  Creates a changeset based on the `model` and `params`.

  If no params are provided, an invalid changeset is returned
  with no validation performed.
  """
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
  end
end

product_controller.ex

  def new(conn, _params) do
    changeset = Product.changeset(
        %Product{variants: [
            %Dumaine.Variant{variant_images: [%Dumaine.VariantImage{}] },
            %Dumaine.Variant{variant_images: [%Dumaine.VariantImage{}] }
          ]
        }
      )
    render(conn, "new.html", changeset: changeset)
  end

  def create(conn, %{"product" => product_params}) do
    changeset = Product.changeset(%Product{}, product_params)

    case Repo.insert(changeset) do
      {:ok, product} ->
        # Product.changeset(product, product_params)
        # |> Repo.update

        conn
        |> put_flash(:info, "Product created successfully.")
        |> redirect(to: product_path(conn, :index))
      {:error, changeset} ->
        render(conn, "new.html", changeset: changeset)
    end
  end

variant.ex

defmodule Dumaine.Variant do
  use Dumaine.Web, :model

  schema "variants" do
    field :price, :integer
    field :sale_price, :integer
    field :available, :integer
    field :sku, :string
    field :delete, :boolean, virtual: true
    belongs_to :product, Dumaine.Product
    has_many :variant_images, Dumaine.VariantImage, on_delete: :fetch_and_delete

    timestamps
  end

  @required_fields ~w(price sale_price available sku)
  @optional_fields ~w(delete)

  @doc """
  Creates a changeset based on the `model` and `params`.

  If no params are provided, an invalid changeset is returned
  with no validation performed.
  """
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
    |> mark_for_deletion()
  end

  defp mark_for_deletion(changeset) do
    if get_change(changeset, :delete) do
      %{changeset | action: :delete}
    else
      changeset
    end
  end
end

variant_image.ex

defmodule Dumaine.VariantImage do
  use Dumaine.Web, :model
  use Arc.Ecto.Model

  schema "variant_images" do
    field :attachment, Dumaine.Attachment.Type
    field :delete, :boolean, virtual: true
    belongs_to :variant, Dumaine.Variant

    timestamps
  end

  @required_fields ~w()
  @optional_fields ~w(delete)

  @required_file_fields ~w()
  @optional_file_fields ~w(attachment)

  @doc """
  Creates a changeset based on the `model` and `params`.

  If no params are provided, an invalid changeset is returned
  with no validation performed.
  """
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
    |> mark_for_deletion()
  end

  def attachment_changeset(model, params \\ :empty) do
    model
    |> cast_attachments(params, @required_file_fields, @optional_file_fields)
    |> mark_for_deletion()
  end

  defp mark_for_deletion(changeset) do
    if get_change(changeset, :delete) do
      %{changeset | action: :delete}
    else
      changeset
    end
  end
end