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smpub2000
 Post subject: one-to-one with foreign key in child table
PostPosted: Fri Nov 21, 2008 10:52 am 
Newbie

Joined: Tue Sep 23, 2008 4:44 pm
Posts: 15
In the example 7.2.2 in hibernate manual, the parent table (PERSON) has foreign key "addressId" of child table. This is reversed, so I want to put the foregin key "personId" in Address table, i.e the Child table should have foreign key of parent.

http://www.hibernate.org/hib_docs/refer ... ional.html

In terms of schema, I want to change the schema from
Code:
create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )



to
Code:
create table Person ( personId bigint not null primary key )
create table Address ( addressId bigint not null primary key,  personId foreign key references Person.personId)




I need to
* do that using a foreign key, not join tables.
* be able to navigate from Person->Address.


What needs to change in the mappings(Person.hbm.xml, Address.hbm.xml) and the code(Person.java, Address.java)? Appreciate any responses.
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christianz
 Post subject:
PostPosted: Fri Nov 21, 2008 12:12 pm 
Newbie

Joined: Wed Oct 08, 2008 1:54 am
Posts: 14
This should be fairly easy to change.
Regarding the java objects not much would have to be done - depending on some requirements if e.g. a Person can have multiple addresses ...

For such a case I'd suggest something like the following:
Code:
class Person {
    private int id;
    private Set<Address> addresses;
}

class Address{
    private int id;
    private Person person;
}


Furthermore you would have to have mapping files containing the following:
Code:
<class name="Person" table="persons" > 
    [id, other field etc ...]
    <set name="addresses" cascade="all" access="field" >
        <key column="person_id" />
        <one-to-many class="Address" />
    </set>
</class>

<class name="Address" table="addresses" > 
    <id name="id" column="id" type="int" access="field">
        <generator class="increment" />
    </id>

    <many-to-one name="person" column="person_id" not-null="true" foreign-key="FK_ADDRESS_PERSON_ID"/>
</class>


I hope that I understood your problem correctly and that I did not inserted too many typos.
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smpub2000
 Post subject:
PostPosted: Fri Nov 21, 2008 1:20 pm 
Newbie

Joined: Tue Sep 23, 2008 4:44 pm
Posts: 15
Thanks for the response. The requirement is also that Person->Address *must* be a one-to-one mapping. Can you please suggest what needs to be modified for one-to-one case.

Code:
class Person {
  Address address;  // an instance of address

}

class Address {
  // address attributes such as street, city etc.
  // Does *NOT* have person reference

}
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christianz
 Post subject:
PostPosted: Fri Nov 21, 2008 2:52 pm 
Newbie

Joined: Wed Oct 08, 2008 1:54 am
Posts: 14
Hmmm if you were using annotations it would be easy because you could just ad a "mappedBy" to the OneToOne annotation of the Person class.
Using mapping-files I searched a bit and found the following issue:
http://opensource.atlassian.com/project ... se/HBX-524
However I was unable to find a reverse one-to-one anywhere in the dtd. Perhaps you would do better using a component ...
THe alternative is to have both entities have each a link to the other one - then you would just add a one-to-one to both mappings.
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smpub2000
 Post subject:
PostPosted: Fri Nov 21, 2008 3:28 pm 
Newbie

Joined: Tue Sep 23, 2008 4:44 pm
Posts: 15
Quote:
THe alternative is to have both entities have each a link to the other one - then you would just add a one-to-one to both mappings.


If I understand correctly, Address class gets changed to have an instance of Parent as below:

Code:
class Address{
  Person person; // an instance of person
  // address attributes

  // getters and setters for person
 
}

If I add this, does this mean that for all instances of Address, I have to call address.setPerson(thePerson) before I can save the person object?

eg:
Code:
Person person = new Person();
Address address = new Address();
person.setAddress(address);
address.setPerson(person);  // need to call this setter?
session.save(person)



can you specify the new mapppings Person.hbm.xml and Address.hbm.xml with the one-to-one mappings?
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smpub2000
 Post subject:
PostPosted: Fri Nov 21, 2008 7:26 pm 
Newbie

Joined: Tue Sep 23, 2008 4:44 pm
Posts: 15
The following mapping (seems to) work for me:

Person.hbm.xml

Code:
<one-to-one name="address"
         class="Address"
         property-ref="person"
         cascade="all"
      />


Address.hbm.xml

Code:
<many-to-one name="person"
      class="Person"
      column="FK_PERSON_ID"
      unique="true"/>



Modified Address.java

Code:
class Address{

  Person person; // added a reference/link to owning entity "Person"
}



Schema
Code:
create table Person ( personId bigint not null primary key )
create table Address ( addressId bigint not null primary key,  FK_PERSON_ID foreign key references Person.personId)
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pvradhakrishna
 Post subject: one-to-one relationship without a foreign key & lazy loa
PostPosted: Thu Dec 04, 2008 3:22 pm 
Regular
Regular

Joined: Tue Feb 19, 2008 6:05 pm
Posts: 82
I have the same issue but the child is loading eagerly in separate select statements for no reason:

I have a user and user_termination tables with only the user_termination having the user_id as the foreign key as the user may or may not be terminated (may not have a user_termination entry)!


I defined the userTermination mapping in user as
Code:
<one-to-one name="userTermination" class="UserTermination"
         property-ref="user" lazy="no-proxy">
</one-to-one>


And the userTermination has a user entry as a many-to-one
Code:
<many-to-one name="participant" class="Participant" column="participant_id" unique="true" not-null="false" />


I chose lazy="no-proxy" in my parent however, whenever I write my HQL on parent User table such as

Code:
from User user where user.user_deleted_date_time is null
it fetches all of my user's first in a single select and then follows by a separate select statements of userTermination, obviously whenever they may only exist, although I don't need them to be fetched eagerly unless I do a left join fetch or something!

Any suggestions?

Regards
Rama
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pvradhakrishna
 Post subject:
PostPosted: Mon Dec 08, 2008 11:13 pm 
Regular
Regular

Joined: Tue Feb 19, 2008 6:05 pm
Posts: 82
Any help on avoiding the eager loading of the one-to-one child objects that too on a separate select?
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