多对一子类外键

Question

I have 2 tables event & location in the public schema. I have two tables in the 'other' schema which inherit from the public tables. There are 4 classes that mimic this setup (Event, Location, OtherEvent, & OtherLocation). I'm trying to use Hibernate to persist the OtherEvent & Other Location.

Every Event has 1+ Locations. A Location is meaningless with an Event.

If I create an OtherEvent and add an OtherLocation to it and try to save it, hibernate inserts the OtherEvent into other.event & hibernate inserts the OtherLocation into other.location (including the event_id). Then hibernate tries to do: UPDATE public.location set event_id=? where location=? This fails because I don't have permission on public.location. How can I prevent it from doing this update? Or change it so it does the update on the other.location table.

I tried modifying public.hbm.xml and changing:

<bag name="locations">

to

<bag name="locations" inverse="true">

This doesn't do the update statement, but the insertion into other.location doesn't include the event_id column (causing a ConstraintViolation on the not null). This would be because the Location doesn't have a reference to the Event object.

I cannot change the DB at all. I am using Hibernate 4. What do I do?

Here is all of the relevant configs: Public Classes:

public class Event{
    private String eventId;
    private List<Location> locations;
    //getters & setters
}

public class Location{
    private String locationId;
    private double lat;
    private double lon;
    //getters and setters
}

Public Tables:

create table public.event{
    event_id varchar PRIMARY KEY,
    event_name varchar,
)

create table public.location(
    location_id varchar PRIMARY KEY,
    event_id varchar NOT NULL, --foreign key to public.event.event_id
    lat double,
    lon double
)

public.hbm.xml:

<hibernate-mapping schema="public">
    <class name="Event" table="event">
        <id name="eventId" column="event_id"/>
        <bag name="locations">
            <key column="event_id" not-null="true"/>
            <one-to-many class="Location">
        </bag>
    </class>
    <class name="Location" table="location">
        <id name="locationId" column="location_id"/>
        <property name="lat" column="lat"/>
        <property name="lon" column="lon"/>
    </class>
</hibernate-mapping>

Other Tables:

create table other.event inherits public.event(
    other_information varchar
)

create table other.location inherits public.location(
    other_loc_information varchar
)

Other Classes:

public class OtherEvent extends Event{
    private String otherInformation;
    //getter & setter
}

public class OtherLocation extends Location{
    private String otherLocInformation;
    //getter & setter
}

other.hbm.xml:

<hibernate-mapping schema="other">
    <union-subclass name="OtherEvent" extends="Event" table="event">
        <property name="otherInformation" column="other_information"/>
    </union-subclass>
    <union-subclass name="OtherLocation" extends="Location" table="location">
        <property name="otherLocInformation" column="other_loc_information"/>
    </union-subclass>
</hibernate-mapping>

Answer 1

I would say that the solution is very close. You said:

I cannot change the DB at all. I am using Hibernate 4. What do I do?

So I expect that you can change the code and mapping. If I am right and you can change the code and mapping: the setting inverse you've tried:

<bag name="locations" inverse="true">

should solve it. Only thing in this case is, that we also have to explicitly assign Location to Event (not only put it into owning collection).

Location should have a property Event

public class Location{
    private String locationId;
    private Event event;
    private double lat;
    private double lon;
    //getters and setters
}

The mapping should be:

<class name="Location" table="location">
  <id name="locationId" column="location_id"/>
  <property name="lat" column="lat"/>
  <property name="lon" column="lon"/>
  <many-to-one name="Event" column="event_id" />
</class>

So if in the code you will do:

event.locations.add(location);
location.event = event;

Then it should work with INSERTS only. The inverse means, that child will do all the stuff alone, so it has to know about parent.