A one-to-one relationship between two tables can be created by:
- Adding a column to the parent table with some unique ID of the child table
- Without any extra column: just inserting the same PK value in both tables
NHibernate supports the second method (correct me) and you can create this relationship using the “foreign” type ID generator and the <one-to-one> tags in both mappings. Today I created the following mappings for two classes named Document and DocumentStatus.
<class name="Document" table="documents">
<id name="Id" column="id">
<generator class="foreign">
<param name="property">Status</param>
</generator>
</id>
<one-to-one name="Status" class="DocumentStatus" constrained="true"/>
... other properties ...
</class>
The trick here is just the foreign ID generator class. Now the mapping for DocumentStatus would be fairly simple.
<class name="DocumentStatus" table="documentstatus">
<id name="Id" column="id">
... any generator class ...
</id>
<one-to-one name="Document" class="Document"/>
... other properties ...
</class>
The classes will have a property of the corresponding type to map this relationship so you can navigate both ways.
class Document {
... other stuff ...
DocumentStatus Status;
}
class DocumentStatus {
... other stuff ...
Document Document;
}
Whenver you insert a new object in Document, the corresponding DocumentStatus object will be created and its PK will be assigned to Document object as well.
Great Stuff!
