Question

i’m certain that i’m missing something really obvious here.
what I want to acheive is quite simple-

I’d like one query to load all Users without hydrating their Posts and Followers collections.
In another query, I do want to initialize these collections, using SubSelect.

using Fetch(..) in the second query would issue left joins, which I don’t want.
I can define those collections’ fetching strategies in the mappings like so (fluently):

.Not.LazyLoad()
.Fetch.Subselect()

which would cause the second query to run the way I want it to, but then I can’t turn off the .Not.LazyLoad() for the first query (i’ve tried .Fetch(u => u.Posts).Lazy but that doesn’t seem to do anything).

what am I missing?

Answer 1

I normally set lazy=true in my mappings (Ayende wrote about it) cause I prefer to control the behaviors in my code.

Doing so your associations will be hydrated only if you require them.

var users = session.QueryOver<User>()
    .List();

Will load all your users but won’t load their posts, unless you access an element of the collection:

var postTitle = users[0].Posts[0].Title;

If you want to load some users and their posts you can simply do something like this:

Post posts = null;

var users = session.QueryOver<User>()
    .Where(x => x.Name == "Jamie")
    .Inner.JoinAlias(t => t.Posts, () => posts)
    .List();

or:

Post posts = null;

var users = session.QueryOver<User>()
    .Where(x => x.Name == "Jamie")
    .Inner.JoinQueryOver(t => t.Posts, () => posts)
    .List();

As you might have noticed using Fetch Eager:

var users = session.QueryOver<User>()
    .Where(x => x.Name == "Jamie")
    .Fetch(x=>x.Posts).Eager
    .List();

uses an outer join which you do not want.

The previous two examples will have a problem you’ve mentioned in your comment.
If you want to avoid cartesian products in your result with QueryOver you can use .TransformUsing(Transformers.DistinctRootEntity) :

Post posts = null;

var users = session.QueryOver<User>()
    .Where(x => x.Name == "Jamie")
    .Inner.JoinAlias(t => t.Posts, () => posts)
    .TransformUsing(Transformers.DistinctRootEntity)
    .List();

You can find lot more information here.