Nhibernate StatelessSession and Lazy Loading

Question

I recently tried to develope a "SessionWrapper". The idea behind it was to be able to switch from a Stateful Session to a Stateless Session easily, with no modifications to the DAOs and the XML mapping files.

Mapping looks like this:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Domain" assembly=Domain">
  <class name="BatchScheduling" table="dbo.batch_scheduling">
    <id name="ID" column="batch_scheduling_id">
      <generator class="native" />
    </id>

    <property name="Name" column="batch_scheduling_name" not-null="true" />
    <property name="Description" column="batch_scheduling_description" not-null="true" />
    <property name="Type" column="batch_scheduling_type" not-null="true" />
    <property name="Cron" column="batch_scheduling_cron" not-null="true" />
    <property name="DateModified" column="batch_scheduling_date_modified" not-null="true" />

    <bag name="Parameters" cascade="all" table="dbo.batch_scheduling_parameters" lazy="true" inverse="true">
      <key column="batch_scheduling_id"/>
      <one-to-many class="BatchSchedulingParameter"/>
    </bag>

  </class>
</hibernate-mapping>

I knew that Stateless Sessions do not support lazy loading. I expected the session to eager fetch all the related objects/collections declared in the mapping.

However, when I try to access BatchScheduling.Parameters I get the following exception:

NHibernate.LazyInitializationException: Initializing[Domain.BatchScheduling#22]-failed to lazily initialize a collection of role: Domain.BatchScheduling.Parameters, no session or session was closed

Any idea?

Answer 1

I knew that Stateless Sessions do not support lazy loading. I expected the session to eager fetch all the related objects/collections declared in the mapping.

That could result in the entire database being loaded into memory, and will in probably 80-90% of cases result in way more queries than are necessary and basically render the stateless session useless.

One approach you can use is to eagerly fetch the relationships you need, using something like SetFetchMode