NHibernate: QueryOver<> help

Question

I\'m just starting out with NHibernate and I\'m having trouble with running more complex queries.

I have entities with a list of tags attached. The user will provide two

Answer 1

That query isn't trivial (have a think about how you might do this using raw SQL). I think the following will work (requiring two correlated sub-queries):

Display displayAlias = null;

var countIncludedTagsSubquery =
    QueryOver.Of<Display>()
        .Where(d => d.Id == displayAlias.Id)
        .JoinQueryOver<DisplayTag>(d => d.Tags)
            .WhereRestrictionOn(t => t.Id).IsInG(includedTagIds)
            .Select(Projections.RowCount());

var excludedTagsSubquery =
    QueryOver.Of<Display>()
        .Where(d => d.Id == displayAlias.Id)
        .JoinQueryOver<DisplayTag>(d => d.Tags)
            .WhereRestrictionOn(t => t.Id).IsInG(excludedTagIds)
            .Select(t => t.Id);

var displays =
    session.QueryOver<Display>(() => displayAlias)
        .WithSubquery.WhereValue(includedTagIds.Count).Eq(countIncludedTagsSubquery)
        .WithSubquery.WhereNotExists(excludedTagsSubquery)
        .List();