When to use inverse=false on NHibernate / Hibernate OneToMany relationships?

by

As Matthieu says, the only case where you wouldn’t want to set inverse = true is where it does not make sense for the child to be responsible for updating itself, such as in the case where the child has no knowledge of its parent.

Lets try a real world, and not at all contrived example:

<class name="SpyMaster" table="SpyMaster" lazy="true">
  <id name="Id">
    <generator class="identity"/>
  </id>
  <property name="Name"/>
  <set name="Spies" table="Spy" cascade="save-update">
    <key column="SpyMasterId"/>
    <one-to-many class="Spy"/>
  </set>
</class>

<class name="Spy" table="Spy" lazy="true">
  <id name="Id">
    <generator class="identity"/>
  </id>
  <property name="Name"/>
</class>

Spymasters can have spies, but spies never know who their spymaster is, because we have not included the many-to-one relationship in the spy class. Also (conveniently) a spy may turn rogue and so does not need to be associated with a spymaster. We can create entities as follows:

var sm = new SpyMaster
{
    Name = "Head of Operation Treadstone"
};
sm.Spies.Add(new Spy
{
    Name = "Bourne",
    //SpyMaster = sm // Can't do this
});
session.Save(sm);

In such a case you would set the FK column to be nullable because the act of saving sm would insert into the SpyMaster table and the Spy table, and only after that would it then update the Spy table to set the FK. In this case, if we were to set inverse = true, the FK would never get updated.

More Related Contents:

  1. What are the First and Second Level caches in (N)Hibernate?
  2. NHibernate configuration for uni-directional one-to-many relation
  3. Hibernate throws MultipleBagFetchException – cannot simultaneously fetch multiple bags
  4. How to Eager Load Associations without duplication in NHibernate?
  5. What is “the inverse side of the association” in a bidirectional JPA OneToMany/ManyToOne association?
  6. Criteria.DISTINCT_ROOT_ENTITY vs Projections.distinct
  7. Fighting cartesian product (x-join) when using NHibernate 3.0.0
  8. What’s the difference between session.Merge and session.SaveOrUpdate?
  9. What is the difference between cascade & inverse in hibernate, what are they used for?
  10. JSON.NET and nHibernate Lazy Loading of Collections
  11. List vs Set vs Bag in NHibernate
  12. JPA OneToMany and ManyToOne throw: Repeated column in mapping for entity column (should be mapped with insert=”false” update=”false”)
  13. Deleted object would be re-saved by cascade (remove deleted object from associations)
  14. nHibernate mapping to custom types
  15. IndexOutOfRangeException Deep in the bowels of NHibernate
  16. Is this the right way to eager load child collections in NHibernate
  17. inverse=true in JPA annotations
  18. Unable to cast object of type NHibernate.Collection.Generic.PersistentGenericBag to List
  19. Hibernate unidirectional one to many association – why is a join table better?
  20. How to create OR statements for NHibernate?
  21. Binary Blob truncated to 8000 bytes – SQL Server 2008 / varbinary(max)
  22. How to save a child with assigned id in nhibernate
  23. Generate XML mappings from fluent Nhibernate
  24. What is the difference between JoinQueryOver and JoinAlias?
  25. How do I view the SQL that is generated by nHibernate?
  26. Get Distinct result set from NHibernate using Criteria API?
  27. Why doesn’t Entity Framework support ODBC?
  28. NHibernate: difference between Interceptor and Listener
  29. What exactly is “persistence ignorance”?
  30. Syntax to define a NHibernate Filter with Fluent Nhibernate?

Leave a Comment