Hi,

I have an entity called Material. It can have many Rental, but only one active at a time (Rental has a column named active = 0/1).
Can I map that using @OneToOne? I'm only interested in the active (if there is one) Rental.

I've tried this in Material:

But that has caused problems with some Materials that have many non-active Rental (and none active):

This mapping is important for a query like this:

(Basically, this is just retrieving all materials created or rented in a certain month).

I've seen there are @Where, @Filter and @Formula annotations, but I couldn't find good explanation or examples about their usage.


Thanks.

I would try with following:



Anyway it is something weird to map a one-to-many relationship as one-to-one,
I personally would not do it, because of the risk encountering problems in future which were not visible immediately.
Furthermore the schema doesn't change if you map it as one-to-many with the mappedBy attribute,
so in theory any sql-statement should work in identical way.

I've tried that before, but was not sucessful. As you said, it only acts in the SQL statement. The relationship is still many-to-one. Same for @Filter.
I'll keep it that way.

I didn't know those where clauses in my HQL would be applied to each element in the collection. So the query is still ok.

Thanks.