cascade.js

const ShopSchema = new Schema({ /** definitions */})

ShopSchema.pre('deleteOne', async function (shop) {
  // Note, don't use arrow function, unless you realize the shop is passed
  // to the middleware instance. Read below:
  
  // right now the document is unclear whether it passes the instance
  // of the object to the middleware or the `this` is the instance
  // so to test, do this
  
  console.log(shop)
  console.log(this)
  
  // depending on which one works, you know what to do
  // then
  await Product.deleteMany({shop: shop._id}) // Product model, not schema, note this too
})

const ProductSchema = new Schema({ /** definitions */ })

const Shop = mongoose.model('Shop', ShopSchema)
const Product = mongoose.model('Product', ProductSchema)

this is assuming the ProductSchema has the shop field as the id of the original shop

@Otoole311 take a look