Postgres单个外键到不同的表

Question

I have some postgres tables:

Component          Component_A      Component_B
-----------         ------------     ------------
id                  id               id
component_type      type             type
component_id        foo_col          bar_col

I would like Component to be able to reference either Component_A or Component_B , depending on the combination of component_type and component_id . Component_A and Component_B have different structures, so they can't be stored within the same table. In a sense, Component is 1 to 1 with both Component_A and Component_B .

What is the best way to model this in Postgres?

Answer 1

If I have understood you correctly, I would put in Component_A a foreign key for id and type referencing component_type and component_id in Component. Same for Component_B. If you put an ON DELETE CASCADE in those two foreign key, whenever a Component was deleted, their corresponding Component_A or Component_B would be deleted, keeping your database without orphan records on those tables.

If you are looking for the other way around (deleting a record in Component_A and having the corresponding Component deleted), I'm not sure if it can be done with foreign keys, but you can achieve that by using a TRIGGER for DELETE in Component_A and Component_B that takes care of deleting the Component related record.