When is it convenient to use the EntityID field instead of additional tables?

Question

symfony

Hello.
For example:
there is a table Notification (notifications). Notifications can be system (System), there may be notifications related to work on database entities. Accordingly, when receiving a notification, we need to find out its type, and get data based on the type.
The next question is, how would it be more correct: to create additional tables with OneToOne relationships?
notifications:

• - id
  
• - user_id
  
• - created_at
  
• -active
  
• - type (SYSTEM_TYPE, POST_TYPE, COMMENT_TYPE ...)
  

NotificationSystem:

• - id (one-to-one)
  
• - data
  
• - system_type
  

NotificationPost:

• - id (one-to-one)
  
• - post_id
  

NotificationComments:

• - id (one-to-one)
  
• - comment_id
  

-----
Either create one table for all cases with different columns:
Notifications:

• - id
  
• - user_id
  
• - created_at
  
• -active
  
• - type (SYSTEM_TYPE, POST_TYPE, COMMENT_TYPE ...)
  
• - system_type
  
• - post_id
  
• - comment_id
  
• ...
  

------
Either use the EntityId:
Notifications column for additional types:

• - id
  
• - user_id
  
• - created_at
  
• -active
  
• - type (SYSTEM_TYPE, POST_TYPE, COMMENT_TYPE ...)
  
• - system_type
  
• - entity_id("Post23", "Post24", "Comment12", "Comment13" ...)
  

I would like to know your opinion.
*I hope I spelled it right

Answer 1

you need table inheritance and different types of objects for different types of notifications. This is if you take "usually".
ps at the work with the doctrine it is easier to operate with entities and mutual relation of these instead of tables. This is a domain-centric thing, not a data-centric one.