improvement: if "" fails to cast, cast it as nil instead

improvement: ReadActionRequiresActor error
improvement: `ensure_selected` change

lib/ash/changeset/changeset.ex

@@ -211,6 +211,8 @@ defmodule Ash.Changeset do
 
   Datalayers currently are not notified of the `select` for a changeset(unlike queries), and creates/updates select all fields when they are performed.
   A select provided on a changeset simply sets the unselected fields to `nil` before returning the result.
+
+  Use `ensure_selected/2` if you simply wish to make sure a field has been selected, without deselecting any other fields.
   """
   def select(changeset, fields, opts \\ []) do
     if opts[:replace?] do
@@ -220,6 +222,27 @@ defmodule Ash.Changeset do
     end
   end
 
+  @doc """
+  Ensures that the given attributes are selected.
+
+  The first call to `select/2` will *limit* the fields to only the provided fields.
+  Use `ensure_selected/2` to say "select this field (or these fields) without deselecting anything else".
+
+  See `select/2` for more.
+  """
+  def ensure_selected(changeset, fields) do
+    if changeset.select do
+      Ash.Changeset.select(changeset, List.wrap(fields))
+    else
+      to_select =
+        changeset.resource
+        |> Ash.Resource.Info.attributes()
+        |> Enum.map(& &1.name)
+
+      Ash.Changeset.select(changeset, to_select)
+    end
+  end
+
   @doc """
   Ensure the the specified attributes are `nil` in the changeset results.
   """

lib/ash/error/query/read_action_requires_actor.ex

@@ -0,0 +1,16 @@
+defmodule Ash.Error.Query.ReadActionRequiresActor do
+  @moduledoc "Used when an actor is referenced in a filter template, but no actor exists"
+  use Ash.Error.Exception
+
+  def_ash_error([], class: :invalid)
+
+  defimpl Ash.ErrorKind do
+    def id(_), do: Ash.UUID.generate()
+
+    def code(_), do: "actor_required"
+
+    def message(_error) do
+      "actor is required"
+    end
+  end
+end

lib/ash/query/query.ex

@@ -63,6 +63,7 @@ defmodule Ash.Query do
     InvalidLimit,
     InvalidOffset,
     NoReadAction,
+    ReadActionRequiresActor,
     Required
   }
 
@@ -367,7 +368,7 @@ defmodule Ash.Query do
 
   defp add_action_filters(query, action, actor) do
     if Ash.Filter.template_references_actor?(action.filter) and is_nil(actor) do
-      Ash.Query.add_error(query, "Read action requires actor")
+      Ash.Query.add_error(query, ReadActionRequiresActor.exception([]))
     else
       built_filter =
         Ash.Filter.build_filter_from_template(
@@ -597,6 +598,8 @@ defmodule Ash.Query do
   if the source field is not selected on the query/provided data an error will be produced. If loading
   a relationship with a query, an error is produced if the query does not select the destination field
   of the relationship.
+
+  Use `ensure_selected/2` if you simply wish to make sure a field has been selected, without deselecting any other fields.
   """
   def select(query, fields, opts \\ []) do
     query = to_query(query)
@@ -608,6 +611,14 @@ defmodule Ash.Query do
     end
   end
 
+  @doc """
+  Ensures that the given attributes are selected.
+
+  The first call to `select/2` will *limit* the fields to only the provided fields.
+  Use `ensure_selected/2` to say "select this field (or these fields) without deselecting anything else".
+
+  See `select/2` for more.
+  """
   def ensure_selected(query, fields) do
     if query.select do
       Ash.Query.select(query, List.wrap(fields))

lib/ash/resource/change/builtins.ex

@@ -72,4 +72,11 @@ defmodule Ash.Resource.Change.Builtins do
   def select(value) do
     {Ash.Resource.Change.Select, target: value}
   end
+
+  @doc """
+  Passes the provided value into `Ash.Changeset.ensure_selected/2`
+  """
+  def ensure_selected(value) do
+    {Ash.Resource.Change.Select, target: value, ensure?: true}
+  end
 end

lib/ash/resource/change/select.ex

@@ -3,6 +3,10 @@ defmodule Ash.Resource.Change.Select do
   use Ash.Resource.Change
 
   def change(changeset, opts, _) do
+    if opts[:ensure?] do
+      Ash.Changeset.ensure_selected(changeset, opts[:target] || [])
+    else
       Ash.Changeset.select(changeset, opts[:target] || [])
     end
   end
+end

lib/ash/type/type.ex

@@ -356,12 +356,24 @@ defmodule Ash.Type do
         {:ok, value}
 
       :error ->
+        case term do
+          "" ->
+            cast_input(type, nil, constraints)
+
+          _ ->
             {:error, "is invalid"}
+        end
 
       {:error, other} ->
+        case term do
+          "" ->
+            cast_input(type, nil, constraints)
+
+          _ ->
             {:error, other}
         end
     end
+  end
 
   @doc """
   Casts a value from the data store to an instance of the type, or errors