improve handling of relation fields that are not preloaded

CHANGELOG.md

@@ -2,6 +2,15 @@
 
 ## Unreleased
 
+## [0.1.3] - 2021-08-30
+
+### Changed
+
+- Raise `EctoNestedChangeset.NotLoadedError` in case the relation field of a
+  loaded resource is not preloaded.
+- Handle list operations on root level relation fields if the field is not
+  preloaded and the data is not persisted.
+
 ## [0.1.2] - 2021-08-29
 
 ### Fixed

README.md

@@ -12,7 +12,7 @@ Add `ecto_nested_changeset` to your list of dependencies in `mix.exs`:
 ```elixir
 def deps do
   [
-    {:ecto_nested_changeset, "~> 0.1.2"}
+    {:ecto_nested_changeset, "~> 0.1.3"}
   ]
 end
 ```

lib/ecto_nested_changeset.ex

@@ -219,9 +219,14 @@ defmodule EctoNestedChangeset do
   defp nested_update(:append, %Changeset{} = changeset, [field], value)
        when is_atom(field) do
     new_value =
-      case {get_change_or_field(changeset, field), changeset.action} do
-        {%NotLoaded{}, :insert} -> [value]
-        {previous_value, _} -> previous_value ++ [value]
+      case get_change_or_field(changeset, field) do
+        %NotLoaded{} ->
+          if Ecto.get_meta(changeset.data, :state) == :built,
+            do: [value],
+            else: raise(EctoNestedChangeset.NotLoadedError, field: field)
+
+        previous_value ->
+          previous_value ++ [value]
       end
 
     Changeset.put_change(changeset, field, new_value)
@@ -236,9 +241,14 @@ defmodule EctoNestedChangeset do
   defp nested_update(:prepend, %Changeset{} = changeset, [field], value)
        when is_atom(field) do
     new_value =
-      case {get_change_or_field(changeset, field), changeset.action} do
-        {%NotLoaded{}, :insert} -> [value]
-        {previous_value, _} -> [value | previous_value]
+      case get_change_or_field(changeset, field) do
+        %NotLoaded{} ->
+          if Ecto.get_meta(changeset.data, :state) == :built,
+            do: [value],
+            else: raise(EctoNestedChangeset.NotLoadedError, field: field)
+
+        previous_value ->
+          [value | previous_value]
       end
 
     Changeset.put_change(changeset, field, new_value)
@@ -259,9 +269,14 @@ defmodule EctoNestedChangeset do
   defp nested_update(:insert, %Changeset{} = changeset, [field, index], value)
        when is_atom(field) and is_integer(index) do
     new_value =
-      case {get_change_or_field(changeset, field), changeset.action} do
-        {%NotLoaded{}, :insert} -> [value]
-        {previous_value, _} -> List.insert_at(previous_value, index, value)
+      case get_change_or_field(changeset, field) do
+        %NotLoaded{} ->
+          if Ecto.get_meta(changeset.data, :state) == :built,
+            do: [value],
+            else: raise(EctoNestedChangeset.NotLoadedError, field: field)
+
+        previous_value ->
+          List.insert_at(previous_value, index, value)
       end
 
     Changeset.put_change(changeset, field, new_value)

lib/exceptions.ex

@@ -0,0 +1,12 @@
+defmodule EctoNestedChangeset.NotLoadedError do
+  @moduledoc """
+  Raised when a relation field that is updated is not preloaded.
+  """
+  defexception [:field, :message]
+
+  def exception(opts) do
+    field = Keyword.fetch!(opts, :field)
+    message = "field `#{inspect(field)}` is not loaded"
+    %__MODULE__{field: field, message: message}
+  end
+end

mix.exs

@@ -1,7 +1,7 @@
 defmodule EctoNestedChangeset.MixProject do
   use Mix.Project
 
-  @version "0.1.2"
+  @version "0.1.3"
   @source_url "https://github.com/woylie/ecto_nested_changeset"
 
   def project do

test/ecto_nested_changeset_test.exs

@@ -53,6 +53,23 @@ defmodule EctoNestedChangesetTest do
              } = changeset.changes
     end
 
+    test "doesn't raise error if field of unpersisted resource is not loaded" do
+      %Category{id: 1}
+      |> change()
+      |> append_at(:posts, %Post{title: "first"})
+    end
+
+    test "raises error if field of persisted resource is not preloaded" do
+      assert_raise EctoNestedChangeset.NotLoadedError,
+                   "field `:posts` is not loaded",
+                   fn ->
+                     %Category{id: 1}
+                     |> Map.update!(:__meta__, &Map.put(&1, :state, :loaded))
+                     |> change()
+                     |> append_at(:posts, %Post{title: "first"})
+                   end
+    end
+
     test "appends item at a sub field of a new list item" do
       changeset =
         %Category{id: 1, posts: []}
@@ -189,6 +206,23 @@ defmodule EctoNestedChangesetTest do
              } = changeset.changes
     end
 
+    test "doesn't raise error if field of unpersisted resource is not loaded" do
+      %Category{id: 1}
+      |> change()
+      |> prepend_at(:posts, %Post{title: "first"})
+    end
+
+    test "raises error if field of persisted resource is not preloaded" do
+      assert_raise EctoNestedChangeset.NotLoadedError,
+                   "field `:posts` is not loaded",
+                   fn ->
+                     %Category{id: 1}
+                     |> Map.update!(:__meta__, &Map.put(&1, :state, :loaded))
+                     |> change()
+                     |> prepend_at(:posts, %Post{title: "first"})
+                   end
+    end
+
     test "prepends item at a sub field of a new list item" do
       changeset =
         %Category{id: 1, posts: []}
@@ -333,6 +367,23 @@ defmodule EctoNestedChangesetTest do
              } = changeset.changes
     end
 
+    test "doesn't raise error if field of unpersisted resource is not loaded" do
+      %Category{id: 1}
+      |> change()
+      |> insert_at([:posts, 0], %Post{title: "first"})
+    end
+
+    test "raises error if field of persisted resource is not preloaded" do
+      assert_raise EctoNestedChangeset.NotLoadedError,
+                   "field `:posts` is not loaded",
+                   fn ->
+                     %Category{id: 1}
+                     |> Map.update!(:__meta__, &Map.put(&1, :state, :loaded))
+                     |> change()
+                     |> insert_at([:posts, 0], %Post{title: "first"})
+                   end
+    end
+
     test "inserts item at a sub field of a new list item" do
       changeset =
         %Category{id: 1, posts: []}