NHibernate Criteria: howto exclude certain mapped properties/collections?

问题

Here's my (simplified) model: Ticket -> Customer Callback (s)

I have my Ticket mapped so that when it's loaded, the Callbacks are as well.

        base.HasMany<TechSupportCallback>(x => x.Callbacks)  
            .KeyColumn(Fields.TRACKED_ITEM_ID)
            .Not.LazyLoad()
            .Inverse()
            .Cache.ReadWrite();

This is not lazy loading because otherwise I'll get 'no session to load entities' when the web service tries to serialize (and load) the proxy. (Using repositories to fetch data.)

It's also bi-directional .. (in the CallbackMap)

        base.References(x => x.Ticket)
            .Column(Fields.TRACKED_ITEM_ID)
            .Not.Nullable();

---

Now .. we need to show an agent a list of their callbacks - JUST their callbacks. -- When I query using Criteria for the Callbacks, I cannot prevent the Ticket (and subsequently it's entire graph, including other collections) from being loaded. I had previously tried to set FetchMode.Lazy, then iterate each resulting Callback and set Ticket to null, but that seems to be ignored.

             // open session & transaction in using (..)
                var query = session.CreateCriteria<TechSupportCallback>()
                    .SetCacheable(true)
                    .SetCacheRegion("CallbacksByUserAndGroups")
                    .SetFetchMode("Ticket", FetchMode.Lazy) // <-- but this doesn't work!
                    .SetMaxResults(AegisDataContext.Current.GetMaxRecordCount())
                    ;
                rValue = query.List<TechSupportCallback>();
                rvalue.ForEach(x => x.Ticket = null;); // <-- since this is already retrieved, doing this merely prevents it from going back across the wire
                tx.Commit();
             // usings end (..)

Should I be doing this with a projection instead? The problem with that .. is I've not been able to find an example of projections being used to populate an entity, or a list of them -- only to be used as a subquery on a child entity or something similar to restrict a list of parent entities.

I could really use some guidance on this.

---

[EDIT]

I tried using a projection as suggested but:

I'm getting the following: (this was because of a bug, and so I've since stopped using the cache and it works. http://nhibernate.jira.com/browse/NH-1090)

System.InvalidCastException occurred
  Message=Unable to cast object of type 'AEGISweb.Data.Entities.TechSupportCallback' to type 'System.Object[]'.
  Source=NHibernate
  StackTrace:
       at NHibernate.Cache.StandardQueryCache.Put(QueryKey key, ICacheAssembler[] returnTypes, IList result, Boolean isNaturalKeyLookup, ISessionImplementor session)
  InnerException: 

at

 rValue = query.List<TechSupportCallback>();

with the projection list defined like

 // only return the properties we want!
 .SetProjection(Projections.ProjectionList()
     .Add(Projections.Alias(Projections.Id(), ex.NameOf(x => x.ID))) // 
     .Add(Projections.Alias(Projections.Property(ex.NameOf(x => x.ContactID)), ex.NameOf(x => x.ContactID)))
     // ...
  )
  .SetResultTra...;
  rValue = query.List<TechSupportCallback>();

mapped like

    public TechSupportCallbackMap()
    {
        base.Cache.ReadWrite();
        base.Not.LazyLoad();

        base.Table("TS_CALLBACKS");

        base.Id(x => x.ID, Fields.ID)
            .GeneratedBy.Sequence("SEQ_TS_CALLBACKS");

        base.References(x => x.Ticket)
            .Column(Fields.TRACKED_ITEM_ID)
            .Not.Nullable();

        base.Map(x => x.TrackedItemID, Fields.TRACKED_ITEM_ID)
            .Not.Insert()
            .Not.Update()
            .Generated.Always()
            ;
        // ...
     }

回答1:

This sounds like it's a job exactly for projections.

var query = session.CreateCriteria<TechSupportCallback>()
                    .SetCacheable(true)
                    .SetCacheRegion("CallbacksByUserAndGroups")
                    .SetFetchMode("Ticket", FetchMode.Lazy)
                    .SetMaxResults(AegisDataContext.Current.GetMaxRecordCount())
                    .SetProjection(Projections.ProjectionList().
                                         .Add(Projections.Alias(Projections.Id(), "Id")
                                         .Add(Projections.Alias(Projections.Property("Prop"), "Prop")))
                    .SetResultTransformer(Transformers.AliasToBean<TechSupportCallback>())
                    ;

Simply list all the properties you want to include and exclude the Ticket entity. You can even create a POCO class simply for encapsulating the results of this query. Rather than using an existing entity class.

来源：https://stackoverflow.com/questions/6780677/nhibernate-criteria-howto-exclude-certain-mapped-properties-collections