Many to One - Aggregate relationship

[er1cAk]

Hello, first of all, thanks for the awesome work!

I reviewed many discussions but didn't find my case, and I would like to hear other opinions about what would be the best. I will describe my case as best as I can also with solutions that I considered. I'm looking for a solution that will follow DDD.

I have agreed that the User and Company,

• user belongs only to one company (users table has companyId column as FK to the company)
• the company has many users

The project allows the registration of new user

• registered user has role OWNER (handled inside register HTTP controller)
• The owner can create other users for his company
• once a new owner is created (or any different event will happen f.e. approved), I want to create a Company for him

Solutions that I considered/tried

1. Company created by Owner
- Once the Owner logs in, they can fill in data about the company, and the company is created
- Event about the created company is emitted together with owner ID
- The user module has a domain event handler for the creation of the new company and will update the foreign_key that references the company (here I have the problem that I cannot update FK using a company ID that isn't committed, as I'm in the transaction)
2. Creating a company once the new Owner is registered
- once the new user (owner) is registered, automatically create a company too
- Company ID is generated inside the HTTP controller for registration (this is what I don't like about this solution, static method create should generate the ID)
3. Registering company
- registration will create a company
- creation of a company will trigger an event that will have all the data about the owner
- The User aggregate is created based on the event "CompanyCreated", the event has all the data about the user (chosen password, etc)

So that's the solution that I considered, wdyt?

Thank you!

[Sairyss]

• Do you want your users to create a company manually after they log in? Solution 1 is fine.
• Do you want a company/owner created automatically? Both 2 and 3 are fine.

I can't tell which one you should use. Solution depends on your business requirements, so you probably should ask your product owner what registration flow you need (or decide it yourself if it's your personal app).

here I have the problem that I cannot update FK using a company ID that isn't committed, as I'm in the transaction

What's exactly the problem here? You should be able to update foreign keys in a transaction without any problems if you insert company first then foreign key.

Company ID is generated inside the HTTP controller for registration (this is what I don't like about this solution, static method create should generate the ID)

Your controller doesn't have to generate an ID. You can just call a static method on an aggregate which will generate an id, then you just use it, something like:

const company = Company.create(); // <- creates id in a company
const companyId = company.id;

But you will probably have to create a service for it, don't make your HTTP controllers execute your business logic.

[er1cAk]

Thanks for quick answer. Glad to hear that all options follow the idea of DDD.

Regarding the update of FK, I found a bug in my code, I managed to solve it, now solution works. I passed the whole command to CompanyEntity props thus command ID was used in props, later this command ID, was used as the ID of the entity.

Once more thank you for confirming that solutions are correct and for your work!