Preheat oven to 350 degrees F (175 degrees C). Grease and flour a fluted tube pan (such as Bundt®).
Sift flour, baking soda, cinnamon, and salt together in a bowl. Set aside.
Mix sugar, egg, and oil together in another bowl. Stir in the flour mixture just until combined; fold in apple, walnuts, and raisins.
Bake in the preheated oven until a toothpick inserted into the cake comes out clean, about 1 hour.