Ignore binary ecto types when serializing changes (#5)

README.md

@@ -162,6 +162,23 @@ config :paper_trail, item_type: Ecto.UUID,
 
 Remember to edit the types accordingly in the generated migration.
 
+#### Serialization and Ecto types
+
+Ecto uses the schema defined [Ecto types](https://hexdocs.pm/ecto/Ecto.Type.html) and the [Repo adapter](https://hexdocs.pm/ecto/Ecto.Adapter.html) dumpers to serialize data to primitive types, which are then inserted in the database by the adapter.
+
+In PaperTrail, all changes are stored in the `item_changes` field as a map, which will be later converted by the Repo adapter to an equivalent database type, such as json.
+
+Using the same approach as Ecto, PaperTrail serializes these changes using their respective Ecto type and `dump/1` callback. Nevertheless, it can cause issues later when the Repo adapter tries to convert the serialized map to json, since it's not possible to convert binary values to json.
+
+In order to avoid these issues, some Ecto types are ignored by default, as they dump binary values: `[Ecto.UUID, :binary_id, :binary]`
+
+You can also configure additional Ecto types to be ignored:
+
+```elixir
+config :paper_trail,
+  not_dumped_ecto_types: [MyCustomType]
+```
+
 ### Version origin references:
 PaperTrail records have a string field called ```origin```. ```PaperTrail.insert/2```, ```PaperTrail.update/2```, ```PaperTrail.delete/2``` functions accept a second argument to describe the origin of this version:
 ```elixir

lib/paper_trail/serializer.ex

@@ -4,6 +4,10 @@ defmodule PaperTrail.Serializer do
   alias PaperTrail.RepoClient
   alias PaperTrail.Version
 
+  @type options :: PaperTrail.options()
+
+  @default_ignored_ecto_types [Ecto.UUID, :binary_id, :binary]
+
   def make_version_struct(%{event: "insert"}, model, options) do
     originator = RepoClient.originator()
     originator_ref = options[originator[:name]] || options[:originator]
@@ -113,6 +117,7 @@ defmodule PaperTrail.Serializer do
     |> List.first()
   end
 
+  @spec serialize(nil | Ecto.Changeset.t() | struct, options) :: nil | map
   def serialize(nil, _options), do: nil
 
   def serialize(%Ecto.Changeset{data: data}, options), do: serialize(data, options)
@@ -129,19 +134,25 @@ defmodule PaperTrail.Serializer do
     |> Map.new()
   end
 
+  @spec dump_fields!(module, map, module, module) :: Keyword.t()
   defp dump_fields!(schema, changes, dumper, adapter) do
     for {field, value} <- changes do
       {alias, type} = Map.fetch!(dumper, field)
-      {alias, dump_field!(schema, field, type, value, adapter)}
+
+      dumped_value =
+        if(
+          type in ignored_ecto_types(),
+          do: value,
+          else: dump_field!(schema, field, type, value, adapter)
+        )
+
+      {alias, dumped_value}
     end
   end
 
+  @spec dump_field!(module, atom, atom, any, module) :: any
   defp dump_field!(schema, field, type, value, adapter) do
     case Ecto.Type.adapter_dump(adapter, type, value) do
-      {:ok, <<_::128>> = binary} ->
-        {:ok, string} = Ecto.UUID.load(binary)
-        string
-
       {:ok, value} ->
         value
 
@@ -178,4 +189,15 @@ defmodule PaperTrail.Serializer do
         "#{model_id}"
     end
   end
+
+  @spec ignored_ecto_types :: [atom]
+  defp ignored_ecto_types do
+    :not_dumped_ecto_types
+    |> get_env([])
+    |> Kernel.++(@default_ignored_ecto_types)
+    |> Enum.uniq()
+  end
+
+  @spec get_env(atom, any) :: any
+  defp get_env(key, default), do: Application.get_env(:paper_trail, key, default)
 end

priv/uuid_repo/migrations/20170525142613_create_items.exs

@@ -21,5 +21,12 @@ defmodule PaperTrail.UUIDRepo.Migrations.CreateItems do
 
       timestamps()
     end
+
+    create table(:uuid_items) do
+      add :item_id,      :uuid, null: false, primary_key: true
+      add :title,        :string, null: false
+
+      timestamps()
+    end
   end
 end

test/support/uuid_models.exs

@@ -53,6 +53,24 @@ defmodule Item do
   end
 end
 
+defmodule UUIDItem do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:item_id, Ecto.UUID, autogenerate: true}
+  schema "uuid_items" do
+    field(:title, :string)
+
+    timestamps()
+  end
+
+  def changeset(model, params \\ %{}) do
+    model
+    |> cast(params, [:title])
+    |> validate_required(:title)
+  end
+end
+
 defmodule FooItem do
   use Ecto.Schema
   import Ecto.Changeset

test/uuid/uuid_test.exs

@@ -65,6 +65,14 @@ defmodule PaperTrailTest.UUIDTest do
 
       version = Version |> last |> repo().one
       assert version.item_id == item.item_id
+
+      uuid_item =
+        %UUIDItem{}
+        |> UUIDItem.changeset(%{title: "hello"})
+        |> PaperTrail.insert!()
+
+      version = Version |> last |> repo().one
+      assert version.item_id == uuid_item.item_id
     end
 
     test "test INTEGER primary key for item_type == :string" do