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copied!<p>This certainly is possible. The Hibernate (not NHibernate) documentation does a good job of explaining this. <a href="http://docs.jboss.org/hibernate/orm/3.6/reference/en-US/html/collections.html#collections-indexedbidirectional" rel="nofollow">7.3.3. Bidirectional associations with indexed collections</a>. There is an issue in the NHibernate bug tracker to have <a href="http://nhforge.org/doc/nh/en/index.html#collections-bidirectional" rel="nofollow">this error</a> in the documentation corrected: <a href="https://nhibernate.jira.com/browse/NH-3554" rel="nofollow">NH-3554</a></p> <p>Below is a complete example of how to do this...</p> <h1>Example</h1> <h2>Entity Classes</h2> <pre><code>public class Parent { public virtual int Id { get; private set; } private IDictionary<string, Child> _children = new Dictionary<string, Child>(); public virtual IDictionary<string, Child> Children { get { return _children; } private set { _children = value; } } public virtual void AddChild(Child child) { child.Parent = this; _children[child.Name] = child; } } public class Child { public virtual int Id { get; private set; } public virtual Parent Parent { get; protected internal set; } public virtual string Name { get; set; } } </code></pre> <h2>NHibernate Mappings</h2> <pre><code><hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="so" namespace="so.Q3398624"> <class name="Parent"> <id name="Id"> <column name="Id" /> <generator class="hilo" /> </id> <map name="Children" inverse="true" cascade="all-delete-orphan"> <key column="ParentId" /> <index column="Name" type="string" /> <one-to-many class="Child" /> </map> </class> <class name="Child"> <id name="Id"> <column name="Id" /> <generator class="hilo" /> </id> <many-to-one name="Parent" column="ParentId" cascade="save-update" not-null="true" unique-key="U1" /> <property name="Name" not-null="true" unique-key="U1" /> </class> </hibernate-mapping> </code></pre> <h2>Tables</h2> <pre><code>CREATE TABLE dbo.Parent ( Id int NOT NULL PRIMARY KEY ); CREATE TABLE dbo.Child ( Id int NOT NULL PRIMARY KEY, ParentId int NOT NULL, Name nvarchar(255) NOT NULL, FOREIGN KEY (ParentId) REFERENCES dbo.Parent (Id), UNIQUE (ParentId, Name) ); </code></pre> <h2>Insert some records...</h2> <pre><code>var parent = new Parent(); parent.AddChild(new Child { Name = "abc" }); parent.AddChild(new Child { Name = "123" }); session.Save(parent); </code></pre> <h1>Final Notes</h1> <p>Be careful when changing a Child's Name. I think the best approach would be to remove the Child from the Parent, change its name, and finally re-add it to the parent. Otherwise <code>Child.Name</code> and <code>Parent.Children.Keys</code> would be out of sync.</p>

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