There was still an issue with preloading and pointers.

This was actually broken with the refactoring. I added a test to catch
the other place the error was occuring. See the new
TestManyToManyPreloadForNestedPointer test in preload_test.go.

preload.go

@@ -295,11 +295,12 @@ func (scope *Scope) handleManyToManyPreload(field *Field, conditions []interface
 			}
 		}
 	} else {
-		object := scope.IndirectValue()
-		source := getRealValue(object, associationForeignStructFieldNames)
-		field := object.FieldByName(field.Name)
-		for _, link := range linkHash[toString(source)] {
-			field.Set(reflect.Append(field, link))
+		if object := scope.IndirectValue(); object.IsValid() {
+			source := getRealValue(object, associationForeignStructFieldNames)
+			field := object.FieldByName(field.Name)
+			for _, link := range linkHash[toString(source)] {
+				field.Set(reflect.Append(field, link))
+			}
 		}
 	}
 }

preload_test.go

@@ -771,6 +771,9 @@ func TestManyToManyPreloadForPointer(t *testing.T) {
 		panic(err)
 	}
 
+	var got5 Level2
+	DB.Preload("Level1s").First(&got5, "value = ?", "bogus")
+
 	var ruLevel1 Level1
 	var zhLevel1 Level1
 	DB.First(&ruLevel1, "value = ?", "ru")
@@ -783,6 +786,109 @@ func TestManyToManyPreloadForPointer(t *testing.T) {
 	}
 }
 
+func TestManyToManyPreloadForNestedPointer(t *testing.T) {
+	type (
+		Level1 struct {
+			ID    uint
+			Value string
+		}
+		Level2 struct {
+			ID      uint
+			Value   string
+			Level1s []*Level1 `gorm:"many2many:levels;"`
+		}
+		Level3 struct {
+			ID       uint
+			Value    string
+			Level2ID sql.NullInt64
+			Level2   *Level2
+		}
+	)
+
+	DB.DropTableIfExists(&Level3{})
+	DB.DropTableIfExists(&Level2{})
+	DB.DropTableIfExists(&Level1{})
+	DB.Table("levels").DropTableIfExists("levels")
+
+	if err := DB.AutoMigrate(&Level3{}, &Level2{}, &Level1{}).Error; err != nil {
+		panic(err)
+	}
+
+	want := Level3{
+		Value: "Bob",
+		Level2: &Level2{
+			Value: "Foo",
+			Level1s: []*Level1{
+				{Value: "ru"},
+				{Value: "en"},
+			},
+		},
+	}
+	if err := DB.Save(&want).Error; err != nil {
+		panic(err)
+	}
+
+	want2 := Level3{
+		Value: "Tom",
+		Level2: &Level2{
+			Value: "Bar",
+			Level1s: []*Level1{
+				{Value: "zh"},
+				{Value: "de"},
+			},
+		},
+	}
+	if err := DB.Save(&want2).Error; err != nil {
+		panic(err)
+	}
+
+	var got Level3
+	if err := DB.Preload("Level2.Level1s").Find(&got, "value = ?", "Bob").Error; err != nil {
+		panic(err)
+	}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %s; want %s", toJSONString(got), toJSONString(want))
+	}
+
+	var got2 Level3
+	if err := DB.Preload("Level2.Level1s").Find(&got2, "value = ?", "Tom").Error; err != nil {
+		panic(err)
+	}
+
+	if !reflect.DeepEqual(got2, want2) {
+		t.Errorf("got %s; want %s", toJSONString(got2), toJSONString(want2))
+	}
+
+	var got3 []Level3
+	if err := DB.Preload("Level2.Level1s").Find(&got3, "value IN (?)", []string{"Bob", "Tom"}).Error; err != nil {
+		panic(err)
+	}
+
+	if !reflect.DeepEqual(got3, []Level3{got, got2}) {
+		t.Errorf("got %s; want %s", toJSONString(got3), toJSONString([]Level3{got, got2}))
+	}
+
+	var got4 []Level3
+	if err := DB.Preload("Level2.Level1s", "value IN (?)", []string{"zh", "ru"}).Find(&got4, "value IN (?)", []string{"Bob", "Tom"}).Error; err != nil {
+		panic(err)
+	}
+
+	var got5 Level3
+	DB.Preload("Level2.Level1s").Find(&got5, "value = ?", "bogus")
+
+	var ruLevel1 Level1
+	var zhLevel1 Level1
+	DB.First(&ruLevel1, "value = ?", "ru")
+	DB.First(&zhLevel1, "value = ?", "zh")
+
+	got.Level2.Level1s = []*Level1{&ruLevel1}
+	got2.Level2.Level1s = []*Level1{&zhLevel1}
+	if !reflect.DeepEqual(got4, []Level3{got, got2}) {
+		t.Errorf("got %s; want %s", toJSONString(got4), toJSONString([]Level3{got, got2}))
+	}
+}
+
 func TestNestedManyToManyPreload(t *testing.T) {
 	type (
 		Level1 struct {