domain driven design – Product, Category, Attributes modelling in DDD


I’m trying to model online shop catalog using Domain Driven Design.

There are three main concepts I have right now: Product, Category, Attribute.

Attribute is a characteristic of a product. For instance things such as color, weight, number of CPU cores etc. There are attributes which possible values are fixed, for instance “condition” – can be new or used. Some of them are within some range of values, for instance “number of CPU cores”. Some are freely created like “color”.

Category have required attributes which every product within that category needs to have, and optional ones. Categories can have parent categories.

Product belongs to a single category which needs to be a leaf category(no children categories).

Now the problem I have is to model these three concepts as aggregates.

One option is to have three different aggregates: Product, Attribute, Category.

Product will have it’s attribute values(each with parent id to Attribute AR).
Attribute will be in different types(fixed, freely choosen, range).
Category will have a list of IDs of Attributes which are required, and list of IDs

The issue here is that whenever I need to create a new product I would need to check if it has all of the required attributes, check the values, and then store the product. This validation would span three aggregates. Where should it go ? It should be domain service ?

Other option is to have 2 AR. Category, with it’s products and Attributes. The issue here is again validation of correct values for a single attribute added to a product. The other huge issue I see here, is that I should fetch the whole aggregate from the repository. Given that category can have hundreds of products, I don’t think that’s a good idea. However it makes sense as a conceptual whole, as If I would like to delete a category, all of it’s products should be deleted as well.

What I am missing here ?