batch-size for efficient eager loading of collection object graph in nhibernate

Question

I want to eager load a collection of objects efficiently. The following code sample shows what I'm doing now. But the c.CommunicationMethods & c.Roles objects are loaded 1 Sql statement at a time. I saw references to the bag & batch-size... can someone provide sample mapping file references? Is that my best option? Can I keep my loop here & batch my sql statements?

Both CommunicationMethods & Roles are defined as many-to-one in the Contacts mapping file.

NHibernateUtil.Initialize(entity.Collection1);
NHibernateUtil.Initialize(entity.Collection2);

NHibernateUtil.Initialize(entity.Contacts);
foreach (var c in entity.Contacts)
{
NHibernateUtil.Initialize(c.CommunicationMethods);
NHibernateUtil.Initialize(c.Roles);
}

I'm not sure what you mean. Do you mean this: .SetFetchMode("CommunicationMethods", FetchMode.Eager) ? If not, can you point me to an example? — Mr Smith
– Mr Smith, Commented Jul 13, 2012 at 13:22

Firo · Accepted Answer · 2012-07-13 14:08:01Z

4

instead of Initialize you could specify which collections to initialise while querying and with multiqueries you could hold the cartesian product small.

// load all collection1 into cache
session.QueryOver<Entity>()
    .Where(filter)
    .Fetch(e => e.Collection1).Eager
    .Future();

// load all collection2 into cache
session.QueryOver<Entity>()
    .Where(filter)
    .Fetch(e => e.Collection2).Eager
    .Future();

var results = session.QueryOver<Entity>()
    .Where(filter)
    .Fetch(e => e.Contacts).Eager
    .Fetch(e => e.Contacts.CommunicationMethods).Eager
    .Fetch(e => e.Contacts.Roles).Eager
    .List();

// results contain all entities with initialised collection1, collection2, contacts, contact.role, contact.CommunicationMethod

answered Jul 13, 2012 at 14:08

Firo

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