NHIbernate lazy load a parent object

Question

I have two objects, Case and Note. A Case can have gobs of Notes, like, in the thousands. We are trying to load them asynchronously, in batches, and stream them to the UI so there is no delay waiting for them all to load.

The class/mappings are

public class Case
{
        public virtual IList<Note> Notes { get; protected set; }
}

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SCMS.TAMS.BusinessEntities" namespace="SCMS.TAMS.BusinessEntities">
    <class name="Case" table="Cases">
        <bag name="Notes" inverse="true" cascade="all" lazy="true">
            <key column="CaseID" />
            <one-to-many class="Note" />
        </bag>
    </class>
</hibernate-mapping>

public class Note
{
    public virtual Case Case {get; set;}
    public virtual long CaseId {get; set;}
}

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SCMS.TAMS.BusinessEntities" namespace="SCMS.TAMS.BusinessEntities" default-lazy="true">
    <class name="Note" table="CaseNotes">
        <many-to-one name="Case" column="CaseID"/>
        <property name="CaseId" column="CaseID" />
    </class>
</hibernate-mapping>

Now, when I call

NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Skip(0).Take(10).ToList();

to load the first 10 Notes for Case 123, the thing loads the Case object, which takes about 30 seconds because there's lots of other things on it, and other logic when it gets loaded, etc., none of which I need/want at this time. All I want/need are the 10 Notes.

I've tried all sorts of variations on this mapping and none of them have worked. What am I doing wrong here?

Answer 1

How are you using this query? is it some thing for the UI? liking showing in a grid or something? or are you performing business logic in a component?

Either way you want to project into another object. Your query right now returns a list of notes which is then going to load that parent object per the mappings.

So if you are using this query to send the information to the UI of an asp.net mvc application, project directly into your view model

NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Select(n => new SomeViewModel { Prop1 = n.Prop1, Prop2 = n.Prop2 ...}).Skip(0).Take(10).ToList();

or create an anonymous object

NHibernateSession.Query<Note>().Where(n => n.CaseId == 123).Select n => new { n.Prop1, n.Prop2, ...}).Skip(0).Take(10).ToList();

This will keep the parent object from loading. It also has the added benefit that you are only querying the information you need because the query be limited to the data you are projecting.