Do link tables need a meaningless primary key field?

Question

I am working on a couple of link tables and I got to thinking (Danger Will Robinson, Danger) what are the possible structures of a link table and what are their pro\'s and c

Answer 1

For true link tables, they typically do not exist as object entities in my object models. Thus the surrogate key is not ever used. The removable of an item from a collection results in a removal of an item from a link relationship where both foreign keys are known (Person.Siblings.Remove(Sibling) or Person.RemoveSibling(Sibling) which is appropriately translated at the data access layer as usp_Person_RemoveSibling(PersonID, SiblingID)).

As Mike mentioned, if it does become an actual entity in your object model, then it may merit an ID. However, even with addition of temporal factors like effective start and end dates of the relationship and things like that, it's not always clear. For instance, the collection may have an effective date associated at the aggregate level, so the relationship itself may still not become an entity with any exposed properties.

I'd like to add that you might very well need the table indexed both ways on the two foreign key columns.