write first test and let changeset errors return error json in controller

lib/entendu/links/link.ex

@@ -2,6 +2,8 @@ defmodule Entendu.Links.Link do
   use Ecto.Schema
   import Ecto.Changeset
 
+  @primary_key {:id, Ecto.UUID, autogenerate: true}
+
   schema "links" do
     field :burn_after_reading, :boolean, default: false
     field :expires, :utc_datetime
@@ -16,7 +18,13 @@ defmodule Entendu.Links.Link do
   @doc false
   def changeset(link, attrs) do
     link
-    |> cast(attrs, [:expires, :burn_after_reading, :filename, :filetype, :text_content, :file_content])
-    |> validate_required([:expires, :burn_after_reading, :filename, :filetype])
+    |> cast(attrs, [
+      :expires,
+      :burn_after_reading,
+      :filename,
+      :filetype,
+      :text_content,
+      :file_content
+    ])
   end
 end

lib/entendu_web/controllers/fallback_controller.ex

@@ -0,0 +1,10 @@
+defmodule EntenduWeb.FallbackController do
+  use EntenduWeb, :controller
+
+  def call(conn, {:error, %Ecto.Changeset{} = changeset}) do
+    conn
+    |> put_status(:unprocessable_entity)
+    |> put_view(EntenduWeb.ChangesetView)
+    |> render("error.json", changeset: changeset)
+  end
+end

lib/entendu_web/controllers/link_controller.ex

@@ -9,27 +9,33 @@ defmodule EntenduWeb.LinkController do
   alias Entendu.Links
   alias Links.Link
   alias Ecto.Changeset
+  alias EntenduWeb.FallbackController
+
+  action_fallback(FallbackController)
 
   def just_page(conn, _params) do
     render(conn, "just.html")
   end
 
-  defparams first_step %{
-    burn_after_reading: [field: :boolean, default: false],
-    expires: :utc_datetime,
-    filename: :string,
-    filetype: :string,
-    text_content: :string,
-    file_content: :string
-  }
+  defparams(
+    first_step(%{
+      burn_after_reading: [field: :boolean, default: false],
+      expires: :utc_datetime,
+      filename: :string,
+      filetype: :string,
+      text_content: :string,
+      file_content: :string
+    })
+  )
 
   def just(conn, params) do
     with %Changeset{valid?: true} = changeset <- first_step(params),
-        link_params <- Params.to_map(changeset),
-        {:ok, %Link{} = link} <- Links.create_link(link_params) do
+         link_params <- Params.to_map(changeset),
+         {:ok, %Link{} = link} <- Links.create_link(link_params) do
       conn
+      |> put_status(:created)
       |> assign(:link, link)
-      |> render("show_authorized", link: link)
+      |> render("show_authorized.json", %{link: link})
     end
   end
 

lib/entendu_web/views/changeset_view.ex

@@ -0,0 +1,15 @@
+defmodule EntenduWeb.ChangesetView do
+  use EntenduWeb, :view
+
+  def translate_errors(%Ecto.Changeset{} = changeset) do
+    Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
+  end
+
+  def translate_errors(errors = %{}), do: errors
+
+  def render("error.json", %{changeset: changeset}) do
+    # When encoded, the changeset returns its errors
+    # as a JSON object. So we just pass it forward.
+    %{errors: translate_errors(changeset)}
+  end
+end