I've got a one-to-one relationship, like a Customer and its Address:

I'd like the object graph to be navigable only from Customer to its Address (the other way makes no sense).

Unfortunately, the existing database model (which cannot be changed) implements the relationship as a "fake" foreign key from the Address to the primary key of the Customer. Fake, because there is actually no foreign key constraint applied, but it could.

Is this situation mappable and how?

I started with <one-to-one name="address" class="Address" cascade="all" outer-join="auto" constrained="false"/> in the Customer.hbm.xml. On the side of the Address, I don't want any getters/setters, so I can't define anything in the mapping descriptor, right?

Regards,

Andreas

You could try a <many-to-one> in the Customer mapping or use a component.

Can components also exist in other tables (I tought only in the same table as the parent)? Could you give an example, please?

Regards,

Andreas

Eh, I was thinking about composite-elements. Forget that :)

It is my understanding that composite elements only have to do with Collections, respectively associations with greater multiplicities than one.

In my case, I've got only a One-to-One relationship: A Customer can have only one Address, and an Address only belongs to one Customer.

Could you give an example of how to use composite elements in my case, please?

Regards,

Andreas

Components wont work in your case, my fault. Try a <many-to-one>

Regarding your "many-to-one"-hint in your first reply:

<many-to-one/> expects a mapped column on the "many" end.

If I were able to tie the many end to the Customer, from the view of the Customer the multiplicity would be 1 (and the other direction is not navigable). I could substitute one-to-one by many-to-one in this case.

Unfortunately, my mapped column (customer_id) is on the Address end. I can't tie the "many" end to the Address, because then the multiplicity would be n (many) from view of the Customer.

Is this correct?

The <many-to-one> on the Customer does what you want.

I just tried your example, but I got an "ORA-00904: invalid column name". I think this happens because column specifies a foreign key column on the parent side, not on the associated side.

You have to put this column (that is in the ADDRESS table) as the column for the many-to-one. I don't know if its really called CUSTOMER_ID, but this is what you described. If it doesn't have a foreign key constraint, you have a broken relational model, but as long as it has the Customers primary key in that column, it should at least work.

This is actually not true. The column gets created in the CUSTOMER table not the ADDRESS table.

How can you reverse this situation when you have a 1->0or1 OR a 1->M unidirectional relationship?

to follow up to my previous post...this can be seen in the docs too. How can I reverse this situation and get the foreign key in the Adress table? A <one-to-many> tag outside a collection type thing?

Thanks!

7.2.2. one to one

A unidirectional one-to-one association on a foreign key is almost identical. The only difference is the column unique constraint.

<class name="Person">
<id name="id" column="personId">
<generator class="native"/>
</id>
<many-to-one name="address"
column="addressId"
unique="true"
not-null="true"/>
</class>

<class name="Address">
<id name="id" column="addressId">
<generator class="native"/>
</id>
</class>

create table Person ( personId bigint not null primary key, addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )

Hate to bottom post,

but does not one know how to do a one-to-one unidirectional relationship with the foreign key in the 'child'?