Can an aggregate have lite version of another aggregate just for read?
I have an order aggregate with Order as root having multiple OrderLine. OrderLine has "identity reference" to Product aggregate. But having only "identity reference" is not enough. I need value of "taxable" property, last "price" property for calculating price in OrderLine. In fact, in order to calculate price in OrderLine, some data from Product aggregate is needed. How can this problem is resolved in DDD? Is it valid in DDD approach to have a lite version of Product (ProductLite) to use as read-only DTO?
-- UPDATE (thanks to @Francesc Castells)
// app service to add OrderLine
product = productRepo.Read(productId)
orderItemPrice = priceDomainService.CalculatePrice(product.price, product.tax)
order.AddOrderLine(product.ID, orderItemPrice)
orderRepo.Save(order)
Yes, this is perfectly valid. An aggregate should store all data that it needs to fulfill its purpose. This data doesn't have to always be user input, it can also come from other aggregates. There's abviously a difference between data produced by an aggregate and data consumed by it. For example, your Order consumes product prices, but it cannot change the product price and expect the rest of the system to respect that new price, as it doesn't own it.
In your scenario, I would say that once in the OrderLine, the Price is not part of the Product anymore, but part of the OrderLine itself, which could probably be defined as the price of the product the moment it was ordered or maybe the moment it was put in the shopping cart.
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