问题
I have a problem. Imagine this data model:
[Person] table has: PersonId, Name1
[Tag] table has: TagId, TagDescription
[PersonTag] has: PersonId, TagId, IsActive
Since [PersonTag] isn't just a simple many-to-many join table, I have all three entities created in nHibernate (exactly like they are in the data model). PersonTag, therefore, needs a composite-id, which I have mapped to a class like this:
<composite-id name="PersonTagKey" class="PersonTagKey">
<key-property name="PersonId"></key-property>
<key-property name="TagId"></key-property>
</composite-id>
I want to traverse the object graph and be able to look at both the Person and Tag objects from a retrieved PersonTag object. So, I have properties on the PersonTag object to do that, mapped like this:
<many-to-one name="Person" column="PersonId" lazy="proxy" cascade="none" class="Person"/>
<many-to-one name="Tag" column="TagId" lazy="proxy" cascade="none" class="Tag"/>
When I try to create a PersonTag object and save it, I get an "Invalid index n for this SqlParameterCollection with Count=n" error. I know this is because I've mapped the PersonId and TagId properties twice, once for the composite-id, and once for the many-to-one relationship. If I don't map the many-to-one objects, then everything works fine.
Is there some way for me to be able to have a composite-id AND a many-to-one relationship based on the same column modeled in the same nHibernate entity?
回答1:
Kay, here's the answer. Little-to-no documentation on this:
<composite-id name="PersonTagKey" class="PersonTagKey">
<key-many-to-one name="Person" column="PersonId" lazy="proxy" class="Person">
<key-many-to-one name="Tag" column="TagId" lazy="proxy" class="Tag"/>
</composite-id>
This will allow you to create a composite-id made up of the inverse of a many-to-one relationship.
Good hunting...
来源：https://stackoverflow.com/questions/497548/nhibernate-2-0-mapping-a-composite-id-and-many-to-one-relationship-causes-i