Am I breaking my aggregate boundaries in this model?

Question

I'm modeling a very basic ASP.NET MVC app using NHibernate and I seem to be stuck on my design. Here's a sketch of my model:

As you can see this is VERY basic but I have some concerns about it. The User root entity and the Organization root entity are accessing the same Organization_Users entity child via two one-to-many relationships. This doesn't seem right and I think I am breaking the aggregate boundaries. This model smells to me but I like the idea because I would like to have code like this:

var user = userRepository.Load(1);
var list = user.Organizations; // All the organizations the user is a part of.

and

var org = orgRepository.Load(1);
var list = org.Users; // All the users in an organization.

Also the extra data in the table like flagged and role would be used by the Organization entity. Is this a bad design? If you have any thoughts that would be great. I'm still trying to get my mind around the thinking of DDD. Thanks

Answer 1

This is a typical Many-To-Many relationship. And the Organization_Users tables is the bridge table. Infact NHibernate and all the other ORM tools have built-in feature to support bridge table.

This thing should be resolved at data modelling level rather than at application level. You should analyze your data model and it is recommended to avoid many-to-many relationships (in the sense if it is not the necesity of domain model, you should try to avoid many-to-many relationship).

First thing first you need to be sure that many-to-many relationship in data model is necessary for mapping domain entities. Once you have done this then the model represented in your diagram is ok for mapping those relationships at application level

Answer 2

I have used an approach similar to your first model on several occasion. The one catch with this approach is that you need to create an OganizationUser class in your domain to handle the Role and Flagged fields from you Domain. This would leave you with something like this in your code.

var user = userRepository.Load(1);
var list = user.OrganizationUsers; // All the organizations the user is a part of including their role and flagged values.

var organization = list[0].Organization; 

*If you're going to be iterating through all a users organizations quite often you'd likely want to eager load the Organization entity along with OrganzitionUser

With the second design you submitted it looks like you would be able to add a user to the OrgUserDetails without adding the user to OrganizationUser. That doesn't seem like something I would want to support from my Domain.