NHibernate One-To-One Mapping

Question

I\'m new to NHibernate so have had limited exposure to mappings etc so far, and I\'ve just hit a scenario which I need some help with.

I have 2 tables:

Reviews T

Answer 1

Ayende has a good explanation for one-to-one mappings here.

In your case the mappings should probably look like this:

Review.hbm.xml

<class xmlns="urn:nhibernate-mapping-2.2" name="Review" table="Reviews">
    <id name="ReviewId" unsaved-value="0">
        <column name="ReviewId"></column>
        <generator class="native" />
    </id>

    <property name="Title" not-null="true" />
    <property name="Descrip" not-null="true" />
    <one-to-one name="TaggedReview"
                      constrained="true"
                      foreign-key="none" 
                      class="TaggedReview" /> 
<!-- foreign-key="none", to prevent circular reference at insert -->
</class>

TaggedReview.hbm.xml

You will most likely need a primary key in the table, because you can't use the same column for the key and the foreign key.

<class xmlns="urn:nhibernate-mapping-2.2" name="TaggedReview" table="TaggedReviews">
    <id name="SomeOtherId">
        <column name="SomeOtherId"></column>
        <generator class="native"/>
    </id>
    <many-to-one name="Review" 
                 unique="true"
                 class="Review"> <!-- Use many-to-one for a foreign key -->
      <column name="ReviewId" />
    </many-to-one>
    <property name="TaggedReviewDescrip" not-null="true" />
</class>

If you cannot or do not want to change the db, you can take a look at NHibernate mapping - one-to-one (or one-to-zero).