have two tables as following Post table and Commen...

# announcements

[rajesh]

have two tables as following
Post table and Comment table
I need to create another table called Activity table which will store aggregate values of likes performed on post or comment. I want to use activity id column which must be EITHER post id or comment id. How do i do enforce this condition in database? (preferably hibernate)

[diesieben07]

I think the simplest way is to have two columns, one for post, one for comment. And either can be null. Then you can use a CHECK to enforce that exactly one of them is not null

[Vampire]

Why must them be in one table, not in two?
And can ids be the same?

[rajesh]

@Vampire its a table that keeps likes performed on post or comment. so i need to store either post or comment id as activity id. id could be same, but i can use another column called type. so its not a problem due to composite primary key. problem is, i want to use either post id or comment id as activity id.

[rajesh]

@diesieben07 this could be good, but i was looking for single colum solution if possible

[diesieben07]

you can't have a foreign key on two tables, so its impossible to do properly with a single column.

[rajesh]

if thats the thing, i'll go with your solution. thanks

[Vampire]

In SQL it is not possible, with Hibernate it should work afair.

[Vampire]

With a discriminator column as you already mentioned

[diesieben07]

Anyone who needs to work with your DB outside of hibernate will hate you,if you do that! 😄

[Vampire]

Yeah, but well, sometimes this is wanted. 😄