prevent Things from parenting themselves

Makefile

@@ -19,3 +19,6 @@ init: tangle
 	mix deps.compile
 	mix compile
 	cd assets; npm install
+
+test: tangle
+	mix test

thing_controller.org

@@ -174,7 +174,7 @@ end
 
 ** =:new= and =:insert= present forms for creating Things
 
-=new/2= is pretty simple, it just creates a form with an empty object in it; =insert/2= is also pretty simple, it creates an object that only has a container ID set. 
+=new/2= is pretty simple, it just creates a form with an empty object in it; =insert/2= is also pretty simple, it creates an object that only has a container ID set.
 
 #+begin_src elixir :noweb-ref controller-new
 def new(conn, _params) do
@@ -220,7 +220,7 @@ end
       <%= if @changeset.action do %>
         <div class="alert callout">Please check errors below!</div>
       <% end %>
-      
+
       <%# if it's shown in the UI and the changeset has the ID: %>
       <%= if assigns[:container] && @changeset.changes.container_id do %>
         <%= hidden_input f, :container_id %>
@@ -475,9 +475,9 @@ end
 
 ** NEXT =:move= sets a new =Thing.container=
 
-I'm not sure how to do this yet. I am thinking that this will be the arbitrary place where I'll integrate Phoenix LiveView: a dynamic search field for Things, with some action when I click them. If I build it properly, it can probably be used in the =:index= list too, so that I can have a filtered search of all my shite. 
+I'm not sure how to do this yet. I am thinking that this will be the arbitrary place where I'll integrate Phoenix LiveView: a dynamic search field for Things, with some action when I click them. If I build it properly, it can probably be used in the =:index= list too, so that I can have a filtered search of all my shite.
 
-The =move= action is maybe misnamed -- it's not doing the movement just rendering a form where the user will be able to. 
+The =move= action is maybe misnamed -- it's not doing the movement just rendering a form where the user will be able to.
 
 #+begin_src elixir :noweb-ref controller-move
 def move(conn, %{"id" => id, "filter_str" => filter_str}) do
@@ -521,7 +521,7 @@ def do_move(conn, %{"id" => id, "new_parent" => new_parent}) do
       |> put_flash(:alert, "Changeset save failed: #{inspect(changeset.errors)}")
       |> put_view(PokaIjoWeb.ThingView)
 
-    _ -> 
+    _ ->
       conn
       |> put_flash(:success, "#{t.name} moved!")
   end
@@ -547,7 +547,7 @@ This relies on [[file:../javascript.org][§JavaScript]] to work; =Phoenix.HTML.L
         </div>
       </div>
     <% end %>
-    
+
     <%= for thing <- @things do %>
       <div class="callout grid-x">
         <div class="small-8 medium-10 cell">
@@ -645,6 +645,7 @@ the =:do_move= behavior is also pretty easy to test.
 #+begin_src elixir :tangle test/poka_ijo_web/controllers/thing_controller_test.exs :noweb yes
 defmodule WebControllersThingDoMoveTest do
   use PokaIjoWeb.ConnCase
+
   alias PokaIjo.Thing
   alias WebControllersThingMoveTest
 
@@ -658,6 +659,21 @@ defmodule WebControllersThingDoMoveTest do
     assert Thing.get_by(id: t.id).container_id == container.id
     assert get_flash(conn, :success) =~ "moved!"
   end
+
+  test ":do_move cannot parent an object to itself", %{conn: conn} do
+    %{container: cur_container} = insert()
+
+    {:ok, t} =
+      %{name: "my_test", description: "hi", container_id: cur_container.id}
+      |> PokaIjo.Thing.new()
+      |> PokaIjo.Repo.insert()
+
+    conn = post(conn, "/things/#{t.id}/move", new_parent: t.id)
+
+    assert Thing.get_by(id: t.id).container_id != t.id
+    assert conn.status == 302
+    assert get_flash(conn, :alert) =~ "failed"
+  end
 end
 #+end_src
 

things.org

@@ -99,6 +99,12 @@ These functions aid in the creation and update of Things.
     |> cast(params, all_keys)
     |> cast_assoc(:container)
     |> validate_required(required_keys)
+    |> validate_change(:container_id, fn :container_id, container_id ->
+      cond do
+        thing.id != nil && container_id == thing.id -> [container: "Cannot contain itself."]
+        true -> []
+      end
+    end)
   end
   #+end_src