diffs cardinality many through, inc tests

lib/ecto_diff.ex

@@ -367,7 +367,47 @@ defmodule EctoDiff do
     end
   end
 
-  defp diff_association(previous, current, %{cardinality: :many, field: field, related: struct}, acc, opts) do
+  defp diff_association(
+         previous,
+         current,
+         %{cardinality: :many, through: [through, assoc_field], owner: owner},
+         acc,
+         opts
+       ) do
+    assoc_diff =
+      acc
+      |> Keyword.get_values(through)
+      |> List.flatten()
+      |> Enum.map(& &1[:changes][assoc_field])
+
+    diff =
+      case assoc_diff do
+        [_ | _] = diff ->
+          List.flatten(diff)
+
+        _ ->
+          through_association = owner.__schema__(:association, through).related
+          association = through_association.__schema__(:association, assoc_field)
+
+          diff = diff_association(previous, current, association, acc, opts)
+
+          diff
+          |> Keyword.get_values(assoc_field)
+          |> List.flatten()
+      end
+
+    if no_changes?(diff), do: acc, else: [{assoc_field, diff} | acc]
+  end
+
+  defp diff_association(
+         previous,
+         current,
+         %{cardinality: :many, field: field} = association,
+         acc,
+         opts
+       ) do
+    %{related: struct} = association
+
     primary_key_fields = get_primary_key_fields(struct, opts)
 
     if primary_key_fields == [],
@@ -428,7 +468,9 @@ defmodule EctoDiff do
     keys
   end
 
-  defp no_changes?(%{effect: :changed, changes: map}) when map == %{}, do: true
+  defp no_changes?([_ | _] = changes), do: Enum.any?(changes, &no_changes?/1)
+  defp no_changes?([]), do: true
+  defp no_changes?(%{effect: effect, changes: map}) when map == %{} and effect in [:added, :changed], do: true
   defp no_changes?(_), do: false
 
   defp primary_key_nil?(key), do: Enum.all?(key, fn {_key, value} -> is_nil(value) end)

mix.exs

@@ -83,7 +83,7 @@ defmodule EctoDiff.MixProject do
       {:credo, "~> 1.0", only: [:dev, :test], runtime: false},
       {:dialyxir, "~> 1.1", only: [:dev, :test], runtime: false},
       {:ecto_sql, "~> 3.8", only: [:dev, :test]},
-      {:ecto, "~> 3.8"},
+      {:ecto, "~> 3.10.3"},
       {:ex_doc, "~> 0.28", only: :dev, runtime: false},
       {:excoveralls, "~> 0.14", only: :test},
       {:jason, ">= 1.0.0", only: [:dev, :test]},

priv/repo/migrations/20230915120413_create_resources_toys.exs

@@ -0,0 +1,18 @@
+defmodule EctoDiff.Repo.Migrations.CreateResources do
+  use Ecto.Migration
+
+  def change do
+    create table(:resources) do
+      add :pet_id, references(:pets)
+      add :refid, :uuid
+    end
+
+    create table(:toys) do
+      add :name, :string
+      add :type, :string
+      add :quantity, :integer, default: 1
+      add :resource_id, references(:resources)
+      add :refid, :uuid
+    end
+  end
+end