I am starting out with DDD and understand that aggregate roots are used to ensure transnational consistency. We should not modify multiple aggregates in one application service.
I would like to know however how to deal with the following situation.
I have an aggregate root called Products.
There is also an aggregate root called Group.
Both have Id's, and can be edited independently.
Multiple Products can point to the same Group.
I have an application service that can change a product's group:
ProductService.ChangeProductGroup(string productId, string groupId)
- Check group exists
- Get product from repository
- Set its group
- Write the product back to repository
I also have an application service where the group can be deleted:
1. Get products from repository whose groupId is set to provided groupId, ensure count is 0 or abort
2. Delete group from groups repository
3. Save changes
My question is the following scenario, what would happen if:
In the ProductService.ChangeProductGroup, we check the group exists (it does), then just after this check a separate user deletes the productGroup (via the other GroupService.DeleteGroup). In this case we set a reference to a product which has just been deleted?
Is this a flaw in my design in that i should use a different domain design (adding additional elements if necessary), or would i have to use transactions?