When to add business logic to domain class, not service

Introduction

I was so accustomed to creating all my business logic in my service class when I came across this unraveling news.

For example,

public class Item{
    private int quantity;
}

@RequiredArgsConstructor
public class ItemService{

    private final ItemRepository itemRepository;
    
    public int updateQuantity{
        //buisness logic to update quantity of Item
        //then using Item.setQuantity to update that value
        itemRepository.find
  }
}

A new perspective

From object-oriented perspective, it is best to implement business logic where the data is present in the entity. This is called Domain Model Pattern.

Whereas if most of the business logic is in the Service layer, it is called Transaction script pattern.