Allow validating uploads in handle_changes

Author: JohnDoneth

lib/upload/multi.ex

@@ -83,14 +83,12 @@ defmodule Upload.Multi do
 
   ## Example
 
-  ```elixir
-  defp insert_person(changeset) do
-    Ecto.Multi.new()
-    |> Ecto.Multi.insert(:person, changeset)
-    |> Upload.Multi.handle_changes(:upload_avatar, :person, changeset, :avatar, key_function: &key_function/1)
-    |> Repo.transaction()
-  end
-  ```
+      defp insert_person(changeset) do
+        Ecto.Multi.new()
+        |> Ecto.Multi.insert(:person, changeset)
+        |> Upload.Multi.handle_changes(:upload_avatar, :person, changeset, :avatar, key_function: &key_function/1)
+        |> Repo.transaction()
+      end
 
   ## Options
 
@@ -99,6 +97,7 @@ defmodule Upload.Multi do
   """
   def handle_changes(multi, name, subject, changeset, field, opts \\ []) do
     key_function = key_function_from_opts(opts)
+    validate_function = validate_function_from_opts(opts)
 
     Multi.run(multi, name, fn repo, changes ->
       # This code is run after the record in inserted in the Multi pipeline.
@@ -120,6 +119,7 @@ defmodule Upload.Multi do
             key_function.(record)
           end
         )
+        |> validate_function.(field)
 
       record_changeset.changes
       |> Enum.reduce(Ecto.Multi.new(), fn {changed_field, change}, multi ->
@@ -130,11 +130,25 @@ defmodule Upload.Multi do
       |> repo.transaction()
       |> case do
         {:ok, result} -> {:ok, result["#{field}_attach_blob"]}
-        error -> error
+        {:error, _stage, changeset, _rest} -> {:error, changeset}
       end
     end)
   end
 
+  defp validate_function_from_opts(opts) do
+    case Keyword.get(opts, :validate) do
+      nil ->
+        fn changeset, _field -> changeset end
+
+      validate_function when is_function(validate_function, 2) ->
+        validate_function
+
+      unexpected ->
+        raise ArgumentError,
+              "validate function must be a function of arity 2. Got #{inspect(unexpected)}"
+    end
+  end
+
   defp key_function_from_opts(opts) do
     case Keyword.get(opts, :key_function) do
       nil ->

test/upload/multi_test.exs

@@ -12,6 +12,25 @@ defmodule Upload.MultiTest do
   @path "test/fixtures/image.jpg"
   @upload %Plug.Upload{path: @path, filename: "image.jpg"}
 
+  describe "handle_changes" do
+    test "can validate changes" do
+      changeset = Person.changeset(%Person{}, %{avatar: "test/fixtures/test.txt"})
+
+      {:error, _, changeset, _} =
+        Ecto.Multi.new()
+        |> Ecto.Multi.insert(:insert_person, changeset)
+        |> Upload.Multi.handle_changes(:upload_avatar, :insert_person, changeset, :avatar,
+          key_function: &key_function/1,
+          validate: fn changeset, field ->
+            Upload.Changeset.validate_attachment_type(changeset, field, allow: ["image/jpeg"])
+          end
+        )
+        |> Repo.transaction()
+
+      assert errors_on(changeset)[:avatar] == ["is not a supported file type"]
+    end
+  end
+
   test "upload/3" do
     assert {:ok, person} = insert_person(%{avatar: @upload})
     assert person.avatar_id
@@ -236,9 +255,7 @@ defmodule Upload.MultiTest do
     Ecto.Multi.new()
     |> Ecto.Multi.insert(:insert_person, changeset)
     |> Upload.Multi.handle_changes(:person, :insert_person, changeset, :avatar,
-      key_function: fn user ->
-        "uploads/users/#{user.id}/avatar"
-      end,
+      key_function: &key_function/1,
       canned_acl: :public
     )
     |> Repo.transaction()