Mapping, entity, no table

[Bruno Frascino]

Hello,

I have a class that needs to be mapped, I am using hibernate. But this class doesn't represent any specific table in the database, it contains fields from different tables. I have no idea how to do that, some help!?
Thanks!

[Edvins Reisons]

You can use a Hibernate <join> or a @SecondaryTable annotation.

[Michael Swierczek]

I don't know if this helps, but you can map an SQL view to an entity in your code. I'm not sure which databases support SQL views, I use Postgres.

So if you have the tables
customer (customer_id, name)
transaction (transaction_id, customer_id, date, description)

You can do:

create view most_recent_transaction_view as
select
    c.customer_id,
    c.name,
    t.transaction_id,
    t.date,
    t.description
from customer c 
left join transaction t where t.customer_id = c.customer_id 
    and t.date = 
    (select max (date) from transaction where customer_id = c.customer_id)
;

Then you can map 'most_recent_transaction_view' as an entity. The differences are that you want to treat it as read-only, because of course updates to an SQL view are not supported. You also want to map the entity relationships as simple Entity properties instead of Entities.

e.g. from the example above, you want to map the customer_id as a String or Long, and not as a Customer object.