rich dao

richdao.md

class OrderService {

   CartDto addItem(cartId, productId) {
      var cart = cartRichDao.findById(cardId)
      var prod = productRichDao.findById(productId)
      
      // service layer not allow mutate Cart entity directly, delegate to rich DAO
      var updatedCart = cartRichDao.addItem(cart, prod, clock.instant())
      return updatedCart.toDto()
   }
}

class CartRichDao {

  Cart addItem(cart, product, instant) {
     var updated = cart.addItem(product, instant)

     var itemChanged = cart.diff(updated)

     db.execute("update cart set updatedAt = ? where id = ? ...", updated...)
     //pseudo code, insert or update depends on itemChanged
     db.execute("update item set qty = qty + 1...", itemChanged...)

     //domain event should be in service layer, but this is demo code...
     publisher.publishEvent(itemChanged)
     return updated
  }
}

//immutable entity
record class Cart(long id, List<Item> items, Instant updatedAt) {

   Cart addItem(product, instant) {
     // if item exist
     //  qty+1
     // else
     //  add new item
     return new Cart(this.id, copiedNewItems, instant)
   }

   ItemChanged diff(cart) {
     // compute items diff
     // ...
   }
}