Controller Form

    <.form for={@form} action={~p"/file-upload/form"} method="post" multipart
  class="flex flex-col gap-space-lg w-full max-w-xl"
>
  <.file_upload field={@form[:attachment]} class="file-upload">
    <:label>Attachment</:label>
    <:close>
      <.heroicon name="hero-x-mark" />
    </:close>
    <:error :let={msg}>
      <.heroicon name="hero-exclamation-circle" class="icon" />
      {msg}
    </:error>
  </.file_upload>
  <.action type="submit" class="button ui-accent">Submit</.action>
</.form>

  

    def file_upload_form_page(conn, _params) do
  phoenix_form =
    Phoenix.Component.to_form(%{"attachment" => nil}, as: :file_upload_phoenix, id: "file-upload-phoenix-form")

  render(conn, :file_upload_form_page, phoenix_form: phoenix_form)
end

def file_upload_form_submit(conn, _params) do
  conn
  |> put_flash(:info, "Submitted")
  |> redirect(to: ~p"/file-upload/form#file-upload-form-phoenix")
end

  

    <.form for={@form} action={~p"/file-upload/form"} method="post" multipart
  class="flex flex-col gap-space-lg w-full max-w-xl"
>
  <input type="hidden" name="file_upload_validate[_sent]" value="1" />
  <.file_upload field={@form[:attachment]} class="file-upload">
    <:label>Attachment</:label>
    <:close>
      <.heroicon name="hero-x-mark" />
    </:close>
    <:error :let={msg}>
      <.heroicon name="hero-exclamation-circle" class="icon" />
      {msg}
    </:error>
  </.file_upload>
  <.action type="submit" class="button ui-accent">Submit</.action>
</.form>

  

    changeset = MyApp.Form.FileUploadForm.changeset_validate(%MyApp.Form.FileUploadForm{}, %{})
to_form(changeset, as: :file_upload_validate, id: "file-upload-validate-form")

  

    defmodule MyApp.Form.FileUploadForm do
  use Ecto.Schema
  import Ecto.Changeset

  embedded_schema do
    field :attachment, :map, virtual: true
  end

  def changeset(form, attrs \\ %{}) do
    cast(form, attrs, [:attachment])
  end

  def changeset_validate(form, attrs \\ %{}) do
    form
    |> cast(attrs, [:attachment])
    |> validate_attachment_required()
  end

  defp validate_attachment_required(changeset) do
    upload = get_change(changeset, :attachment)

    if present_upload?(upload) do
      changeset
    else
      add_error(changeset, :attachment, "can't be blank", validation: :required)
    end
  end

  defp present_upload?(%Plug.Upload{filename: name}) when is_binary(name) and name != "", do: true
  defp present_upload?(_), do: false
end

  

    <form action={~p"/file-upload/form"} method="post" enctype="multipart/form-data" class="flex flex-col gap-space-lg w-full max-w-xl">
  <input type="hidden" name="_csrf_token" value={Plug.CSRFProtection.get_csrf_token()} />
  <input type="hidden" name="_file_upload_form" value="native" />
  <.file_upload name="user[avatar]" class="file-upload">
    <:label>Avatar</:label>
    <:close>
      <.heroicon name="hero-x-mark" />
    </:close>
  </.file_upload>
  <.action type="submit" class="button ui-accent">Submit</.action>
</form>

  

    def file_upload_form_submit(conn, %{"user" => %{"avatar" => upload}}) do
  conn
  |> put_flash(:info, "Submitted: avatar=#{file_upload_attachment_label(upload)}")
  |> redirect(to: ~p"/file-upload/form#file-upload-form-native")
end

defp file_upload_attachment_label(%Plug.Upload{filename: name}) when name != "", do: name
defp file_upload_attachment_label(_), do: "(none)"