Eager loading child collection with NHibernate

限于喜欢 提交于 2019-11-29 05:28:32

Found a solution but it isn't pretty. First I go and find all the Invoice IDs, then I use them in the multiquery and then at the end filtering the results through a HashedSet. Because of the large number of items sometimes i couldn't use the normalt Restriction.In and was forced to send it as a string.

Any suggested tweaks?

var criteria = Session.CreateInvoiceBaseCriteria(query, archived)
    .SetProjection(Projections.Id());

var invoiceIds = criteria.List<int>();
if (invoiceIds.Count > 0)
{
    var joinedIds = JoinIDs(criteria.List<int>()); // To many ids to send them as parameters.

    var sql1 = string.Format("from Invoice i inner join fetch i.States where i.InvoiceID in ({0}) order by i.{1} {2}", joinedIds, query.Order, query.OrderType.ToString());
    var sql2 = string.Format("from Invoice i inner join fetch i.AttestationRequests where i.InvoiceID in ({0})", joinedIds);
    var sql3 = string.Format("from Invoice i inner join fetch i.Attestations where i.InvoiceID in ({0})", joinedIds);

    var invoiceQuery = Session.CreateMultiQuery()
        .Add(sql1)
        .Add(sql2)
        .Add(sql3);

    var result = invoiceQuery.List()[0];

    return new UniqueFilter<Invoice>((ICollection)result);
}

return new List<Invoice>();

To answer your question: yes, it results in huge resultsets.

I suggest to:

  • just naively write your queries without eager fetching
  • On certain places, put an eager fetch, but only one per query
  • if you really get performance problems which you can't solve with indexes or by enhance queries and mapping strategies, use your solution with the multiple queries.
tmatuschek

While it might not be exactly what you are looking for, I would recommend looking at this article:

Eager loading aggregate with many child collections

If you look around the rest of that site you will find even more posts that discuss eager loading and other great nHibernate stuff.

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