NHibernate paging criteria with fetchmode eager. (using fluent NH)

问题

Question: How to get an eager loaded criteria to return paged results on the root entity with all child collections set fetchmode = eager.

I am trying to get a 10 item paged result set with eager loaded child collections. The problem is the query does a select top 10 wrapped around the entire select. The causes it to return only the first 10 results including all joined records. If the first entity has 10 child objects then my result set will return 1 entity with 10 child objects loaded. I need the entities and child collections returned hydrated (lazy off). If I turn lazy loading off and run this query I get the n+1 query for each associate in result set.

This is my basic query process:

criteria = context.Session.CreateCriteria<Associate>();
criteria.SetMaxResults(10); //hardcoded for testing
criteria.SetFirstResult(1); //hardcoded for testing
criteria.SetFetchMode("Roles", NHibernate.FetchMode.Eager);
criteria.SetFetchMode("Messages", NHibernate.FetchMode.Eager);
criteria.SetFetchMode("DirectReports", NHibernate.FetchMode.Eager);
criteria.SetResultTransformer(new DistinctRootEntityResultTransformer());
return criteria.List<Associate>();


public AssociateMap()
    {
        ReadOnly();
        Id(x => x.AssociateId);
        Map(x => x.FirstName);
        Map(x => x.LastName);
        Map(x => x.ManagerId);
        Map(x => x.Department);
        Map(x => x.Email);
        Map(x => x.JobTitle);

        Map(x => x.LastFirstName).Formula("LTRIM(RTRIM(LastName)) + ', ' + LTRIM(RTRIM(FirstName))");

        HasMany(x => x.Messages).KeyColumn("AssociateId").Inverse().Cascade.All();
        HasMany(x => x.Roles).Element("RoleKey");
        HasMany(x => x.DirectReports).KeyColumn("ManagerId").Cascade.None().ForeignKeyConstraintName("FK_Associate_Manager");
        //HasMany(x => x.DirectReports).Element("ManagerId").CollectionType(typeof(Domain.Associate));


    }

回答1:

The solution ended up using a subquery to set the max results. I added the subquery using Subqueries.PropertyIn. I am cloning the "criteria" to "limiter" because I added criterion expression in code not shown. So I need to clone these criterion into the subquery so the top 10 select will be in the "IN" statement. Now I can eager load the child collections and add pagination to the root entity to get 10 enties back without issues with cartesian or n+1. I will try to follow up with more complete and organized code.

//criteria = context.Session.CreateCriteria<Associate>(); 
//changed criteria to DetachedCriteria.
criteria = DetachedCriteria.For<Associate>();

DetachedCriteria limiter = CriteriaTransformer.Clone(criteria); 
limiter.SetProjection(Projections.Id());
limiter.SetMaxResults(10);
criteria.Add(Subqueries.PropertyIn("AssociateId", limiter));

criteria.SetFetchMode("Roles", NHibernate.FetchMode.Eager); 
criteria.SetFetchMode("Messages", NHibernate.FetchMode.Eager); 
criteria.SetFetchMode("DirectReports", NHibernate.FetchMode.Eager); 
criteria.SetResultTransformer(new DistinctRootEntityResultTransformer()); 
return criteria.List<Associate>();

来源：https://stackoverflow.com/questions/4329487/nhibernate-paging-criteria-with-fetchmode-eager-using-fluent-nh

标签

fluent-nhibernate

nhibernate-mapping