Creating related entity after Insertion Typeorm

I have 2 Entities:

  1. User
  2. Promo

I would like to create a Promo entity, which has a oneToOne relationship with the User entity, every time a User entity is created/inserted.

I am new to typeorm, so I'm not sure what the best way to achieve this would be.

I have tried using subscribers can't seem to achieve the desired functionality. Another option would be to do this inside the GraphQL Resolver, but this seems messy to me.

What is considered best practice when trying to do this?