Question

I have a search-method which returns multiple items, each with several child-properties with references to other tables.
For the child-property that is a collection everything works as I want it to but how can I do the same for the one-to-one children?

Here is some stubs and some of the code I tried:

public class Request {
    //HasMany(x => x.Examinations).Access.CamelCaseField().Cascade.All().BatchSize(100);
    public virtual IList<Examination> Examinations;

    //References(x => x.Creator, "rem_creator_userid");
    public virtual User Creator { get; private set; }
}

public class RepositoryExample {

    // This search will ask one nice-looking query to the database fetchning all the
    // requests
    // Then it will ask ONE query fetching the Examinations from the database
    // Then it will ask N+1 questions fetching Creator from all Requests
    public IList<Request> Search1(ListRequestSearchConditions searchConditions) {
        var query =
            from request in Session.Query<Request>()
            from exam in request.Examinations
            where
                searchConditions.Units.Contains(request.ReferralSource) &&
                exam.Status.HasValue &&
                exam.Status.Value >= ExaminationStatus.Value.RequestSubmitted &&
                request.PatientId != null
            select request;

        return query
            .Skip((searchConditions.Page - 1) * searchConditions.PageSize)
            .Take(searchConditions.PageSize)
            .ToList();
    }

    // This search with ask one slow join-query fetching everything from the database
    public IList<Request> Search2(ListRequestSearchConditions searchConditions) {
            Examination examinationAlias = null;

        return Session.QueryOver<Request>()
            .WhereRestrictionOn(request => request.ReferralSource).IsIn(searchConditions.Units)
            .Where(request => request.PatientId != null)
            .JoinAlias(request => request.Examinations, () => examinationAlias)
            .Where(() => examinationAlias.Status.Value != null)
            .Where(() => examinationAlias.Status.Value >= ExaminationStatus.Value.RequestSubmitted)
            .Skip((searchConditions.Page - 1) * searchConditions.PageSize)
            .Take(searchConditions.PageSize)
            .ToList();
    }

    // This search will first ask ONE query joining Request with Examinations
    // Then it will ask ONE query fetching the Examinations from the database
    // Then it will ask N+1 queries fetching Creator from all Requests
    public IList<Request> Search3(ListRequestSearchConditions searchConditions) {
            Examination examinationAlias = null;

        return Session.QueryOver<Request>()
            .WhereRestrictionOn(request => request.ReferralSource).IsIn(searchConditions.Units)
            .Where(request => request.PatientId != null)
            .JoinAlias(request => request.Examinations, () => examinationAlias)
            .Where(() => examinationAlias.Status.Value != null)
            .Where(() => examinationAlias.Status.Value >= ExaminationStatus.Value.RequestSubmitted)
            .Fetch(request => request.Examinations).Lazy
            .Fetch(request => examinationAlias.ExaminationType).Lazy;
            .Skip((searchConditions.Page - 1) * searchConditions.PageSize)
            .Take(searchConditions.PageSize)
            .ToList();
    }
}

I hope that is possible to do this in 3 queries, one fetching the list of Requests, one fetching the Examinations and one fetching the Creators.

Answer 1

If you don’t want to have it in one single query (using Fetch/ThenFetch in LINQ) and use batching instead, you have to specify it at Creator mapping level. Batch size can’t be defined at query level.

In Fluent NHibernate you can just add BatchSize(100) in your Creator mapping.