diff --git a/lib/ash_phoenix/form/auto.ex b/lib/ash_phoenix/form/auto.ex
index 62c3705..a51ec38 100644
--- a/lib/ash_phoenix/form/auto.ex
+++ b/lib/ash_phoenix/form/auto.ex
@@ -127,6 +127,29 @@ defmodule AshPhoenix.Form.Auto do
 
       constraints = unwrap_union(type, constraints)
 
+      data =
+        case form_type do
+          :list ->
+            fn parent ->
+              if parent do
+                Map.get(parent, attr.name) || []
+              else
+                []
+              end
+            end
+
+          :single ->
+            fn parent ->
+              if parent do
+                case Map.get(parent, attr.name) do
+                  [value | _] -> value
+                  [] -> nil
+                  value -> value
+                end
+              end
+            end
+        end
+
       updater = fn opts, data, params ->
         {type, constraints} = determine_type(constraints, data, params)
 
@@ -137,31 +160,6 @@ defmodule AshPhoenix.Form.Auto do
             {AshPhoenix.Form.WrappedValue, [], true}
           end
 
-        data =
-          case form_type do
-            :list ->
-              fn parent ->
-                if parent do
-                  Map.get(parent, attr.name) || []
-                else
-                  []
-                end
-                |> Enum.map(&wrap_value(&1, fake_embedded?))
-              end
-
-            :single ->
-              fn parent ->
-                if parent do
-                  case Map.get(parent, attr.name) do
-                    [value | _] -> value
-                    [] -> nil
-                    value -> value
-                  end
-                end
-                |> wrap_value(fake_embedded?)
-              end
-          end
-
         prepare_source =
           if fake_embedded? do
             fn source ->
@@ -207,7 +205,6 @@ defmodule AshPhoenix.Form.Auto do
           prepare_source: prepare_source,
           transform_params: transform_params,
           embed?: true,
-          data: data,
           forms: [],
           updater: fn opts ->
             Keyword.update!(opts, :forms, fn forms ->
@@ -223,6 +220,7 @@ defmodule AshPhoenix.Form.Auto do
 
       {attr.name,
        [
+         data: data,
          type: form_type,
          updater: updater
        ]}
@@ -230,12 +228,6 @@ defmodule AshPhoenix.Form.Auto do
     |> Keyword.new()
   end
 
-  defp wrap_value(value, true) do
-    %AshPhoenix.Form.WrappedValue{value: value}
-  end
-
-  defp wrap_value(value, _), do: value
-
   defp determine_type(constraints, _data, %{"_union_type" => union_type} = params) do
     constraints[:types]
     |> Enum.find(fn {key, _value} ->
@@ -288,24 +280,32 @@ defmodule AshPhoenix.Form.Auto do
   end
 
   defp tags_equal(config, key, params) do
-    case config[:tag_value] || key do
-      value when is_atom(value) ->
-        params[to_string(config[:tag])] == to_string(value) ||
-          params[to_string(config[:tag])] == value
+    if is_map(params) do
+      case config[:tag_value] || key do
+        value when is_atom(value) ->
+          params[to_string(config[:tag])] == to_string(value) ||
+            params[to_string(config[:tag])] == value
 
-      value ->
-        params[to_string(config[:tag])] == value
+        value ->
+          params[to_string(config[:tag])] == value
+      end
+    else
+      false
     end
   end
 
   defp tags_equal_data(config, key, data) do
-    case config[:tag_value] || key do
-      value when is_atom(value) ->
-        data[config[:tag]] == to_string(value) ||
-          data[config[:tag]] == value
+    if is_struct(data) do
+      case config[:tag_value] || key do
+        value when is_atom(value) ->
+          data[config[:tag]] == to_string(value) ||
+            data[config[:tag]] == value
 
-      value ->
-        data[config[:tag]] == value
+        value ->
+          data[config[:tag]] == value
+      end
+    else
+      false
     end
   end
 
diff --git a/lib/ash_phoenix/form/form.ex b/lib/ash_phoenix/form/form.ex
index 1ce260d..eaf4950 100644
--- a/lib/ash_phoenix/form/form.ex
+++ b/lib/ash_phoenix/form/form.ex
@@ -375,8 +375,18 @@ defmodule AshPhoenix.Form do
   def for_action(resource_or_data, action, opts) do
     {resource, data} =
       case resource_or_data do
-        module when is_atom(resource_or_data) -> {module, module.__struct__()}
-        %resource{} = data -> {resource, data}
+        module when is_atom(resource_or_data) ->
+          {module, module.__struct__()}
+
+        %resource{} = data ->
+          if Ash.Resource.Info.resource?(resource) do
+            {resource, data}
+          else
+            {AshPhoenix.Form.WrappedValue, %AshPhoenix.Form.WrappedValue{value: data}}
+          end
+
+        value ->
+          {AshPhoenix.Form.WrappedValue, %AshPhoenix.Form.WrappedValue{value: value}}
       end
 
     type =
@@ -1121,7 +1131,7 @@ defmodule AshPhoenix.Form do
               |> Enum.reduce(forms, fn {params, index}, forms ->
                 case Enum.find(form.forms[key] || [], &matcher.(&1, params, form, key, index)) do
                   nil ->
-                    opts = update_opts(opts, nil, form_params)
+                    opts = update_opts(opts, nil, params)
 
                     new_form =
                       cond do
@@ -3201,6 +3211,7 @@ defmodule AshPhoenix.Form do
               tenant: form.opts[:tenant],
               accessing_from: config[:managed_relationship],
               transform_params: config[:transform_params],
+              prepare_source: config[:prepare_source],
               warn_on_unhandled_errors?: form.warn_on_unhandled_errors?,
               forms: config[:forms] || [],
               data: opts[:data],
diff --git a/lib/ash_phoenix/form/wrapped_value.ex b/lib/ash_phoenix/form/wrapped_value.ex
index e1899eb..2ba7a95 100644
--- a/lib/ash_phoenix/form/wrapped_value.ex
+++ b/lib/ash_phoenix/form/wrapped_value.ex
@@ -15,4 +15,103 @@ defmodule AshPhoenix.Form.WrappedValue do
       primary? true
     end
   end
+
+  changes do
+    change fn changeset, _ ->
+      if Ash.Changeset.changing_attribute?(changeset, :value) do
+        value = Ash.Changeset.get_attribute(changeset, :value)
+
+        with {:ok, casted} <-
+               Ash.Type.Helpers.cast_input(
+                 changeset.context.type,
+                 value,
+                 changeset.context.constraints,
+                 changeset
+               ),
+             {:constrained, {:ok, casted}} when not is_nil(casted) <-
+               {:constrained,
+                Ash.Type.apply_constraints(
+                  changeset.context.type,
+                  casted,
+                  changeset.context.constraints
+                )} do
+          Ash.Changeset.force_change_attribute(changeset, :value, casted)
+        else
+          {:constrained, {:ok, nil}} ->
+            Ash.Changeset.force_change_attribute(changeset, :value, nil)
+
+          {:constrained, {:error, error}, argument} ->
+            add_invalid_errors(value, :attribute, changeset, :value, error)
+
+          {:error, error} ->
+            add_invalid_errors(value, :attributes, changeset, :value, error)
+        end
+      else
+        changeset
+      end
+    end
+  end
+
+  defp add_invalid_errors(value, type, changeset, attribute, message) do
+    messages =
+      if Keyword.keyword?(message) do
+        [message]
+      else
+        List.wrap(message)
+      end
+
+    Enum.reduce(messages, changeset, fn message, changeset ->
+      if is_exception(message) do
+        error =
+          message
+          |> Ash.Error.to_ash_error()
+
+        errors =
+          case error do
+            %class{errors: errors}
+            when class in [
+                   Ash.Error.Invalid,
+                   Ash.Error.Unknown,
+                   Ash.Error.Forbidden,
+                   Ash.Error.Framework
+                 ] ->
+              errors
+
+            error ->
+              [error]
+          end
+
+        Enum.reduce(errors, changeset, fn error, changeset ->
+          Ash.Changeset.add_error(changeset, Ash.Error.set_path(error, attribute))
+        end)
+      else
+        opts = Ash.Type.Helpers.error_to_exception_opts(message, %{name: attribute})
+
+        exception =
+          case type do
+            :attribute -> InvalidAttribute
+            :argument -> InvalidArgument
+          end
+
+        Enum.reduce(opts, changeset, fn opts, changeset ->
+          error =
+            exception.exception(
+              value: value,
+              field: Keyword.get(opts, :field),
+              message: Keyword.get(opts, :message),
+              vars: opts
+            )
+
+          error =
+            if opts[:path] do
+              Ash.Error.set_path(error, opts[:path])
+            else
+              error
+            end
+
+          Ash.Changeset.add_error(changeset, error)
+        end)
+      end
+    end)
+  end
 end
diff --git a/test/auto_form_test.exs b/test/auto_form_test.exs
index 80fb8fc..a30505a 100644
--- a/test/auto_form_test.exs
+++ b/test/auto_form_test.exs
@@ -56,15 +56,15 @@ defmodule AshPhoenix.AutoFormTest do
 
   describe "single unions" do
     test "a form can be added for a union" do
-        Post
-        |> AshPhoenix.Form.for_create(:create,
-          api: Api,
-          forms: [
-            auto?: true
-          ]
-        )
-        |> AshPhoenix.Form.add_form(:union, params: %{"type" => "foo"})
-        |> form_for("action")
+      Post
+      |> AshPhoenix.Form.for_create(:create,
+        api: Api,
+        forms: [
+          auto?: true
+        ]
+      )
+      |> AshPhoenix.Form.add_form(:union, params: %{"type" => "foo"})
+      |> form_for("action")
     end
 
     test "a form can be removed from a union" do
@@ -113,20 +113,72 @@ defmodule AshPhoenix.AutoFormTest do
 
     test "a form can be removed from a union" do
       form =
-      Post
-      |> AshPhoenix.Form.for_create(:create,
-        api: Api,
-        forms: [
-          auto?: true
-        ]
-      )
-      |> AshPhoenix.Form.add_form(:union_array, params: %{"type" => "foo"})
-      |> form_for("action")
+        Post
+        |> AshPhoenix.Form.for_create(:create,
+          api: Api,
+          forms: [
+            auto?: true
+          ]
+        )
+        |> AshPhoenix.Form.add_form(:union_array, params: %{"type" => "foo"})
+        |> form_for("action")
 
       AshPhoenix.Form.remove_form(form, [:union_array, 0])
     end
-  end
 
+    test "validating a form with valid values works" do
+      form =
+        Post
+        |> AshPhoenix.Form.for_create(:create,
+          api: Api,
+          forms: [
+            auto?: true
+          ]
+        )
+        |> AshPhoenix.Form.add_form(:union_array, params: %{"type" => "foo"})
+        |> form_for("action")
+
+      assert %{union_array: [%Ash.Union{value: %{value: "abc"}}]} =
+               form
+               |> AshPhoenix.Form.validate(%{
+                 "text" => "text",
+                 "union_array" => %{
+                   "0" => %{
+                     "type" => "foo",
+                     "value" => "abc"
+                   }
+                 }
+               })
+               |> AshPhoenix.Form.submit!()
+    end
+
+    test "validating a form with an invalid value works" do
+      form =
+        Post
+        |> AshPhoenix.Form.for_create(:create,
+          api: Api,
+          forms: [
+            auto?: true
+          ]
+        )
+        |> AshPhoenix.Form.add_form(:union_array, params: %{"type" => "foo"})
+        |> form_for("action")
+
+      assert_raise Ash.Error.Invalid, ~r/must match the pattern/, fn ->
+        form
+        |> AshPhoenix.Form.validate(%{
+          "text" => "text",
+          "union_array" => %{
+            "0" => %{
+              "type" => "foo",
+              "value" => "def"
+            }
+          }
+        })
+        |> AshPhoenix.Form.submit!()
+      end
+    end
+  end
 
   defp auto_forms(resource, action) do
     [forms: Auto.auto(resource, action)]
diff --git a/test/support/resources/foo.ex b/test/support/resources/foo.ex
index 14e47eb..25fa287 100644
--- a/test/support/resources/foo.ex
+++ b/test/support/resources/foo.ex
@@ -7,6 +7,8 @@ defmodule AshPhoenix.Test.Foo do
       default "foo"
     end
 
-    attribute :value, :string
+    attribute :value, :string do
+      constraints match: ~r/abc/
+    end
   end
 end