Question

这个HQL语句在执行时会产生以下结果：

select t, count(s) from Submission s right join s.Topics as t GROUP BY t.Id

result[0]
    [0] topic_id, topic_name, ... 
    [1] 10

result[1]
    [0] topic_id, topic_name, ... 
    [1] 12
     .
result[n]
    [0] topic_id, topic_name, ... 
    [1] 19

这个DetachedCriteria API产生几乎相似的结果，但没有加载主题

ProjectionList PrjList = Projections.ProjectionList();
PrjList.Add(Projections.GroupProperty("Topics"), "t");
PrjList.Add(Projections.Count("Id"));

DetachedCriteria Filter = DetachedCriteria.For<Submission>();
Filter.CreateCriteria("Topics", "t", JoinType.RightOuterJoin);
Filter.SetProjection(PrjList);

result[0]
    [0] null
    [1] 10

result[1]
    [0] null
    [1] 12
     .
result[n]
    [0] null
    [1] 19

由于某种原因，nhibernate拒绝为结果集创建主题对象，但它确实用于HQL查询。那是为什么？

Answer 1

在http://ayende.com/blog/tags/nhibernate?page=3上查看Ayende博客上的独立标准。它为您提供了关于左外连接和HQL分组的非常详细的分步指南以及背后的映射。

Answer 2

var orderIDsContainingCurrentSku = DetachedCriteria.For<OrderItem>()
    .Add<OrderItem>(x=>x.Product.SKU==sku)
    .SetProjection(Projections.Property("Order.id"));
var skusOfProductsAppearingInOrdersContainingCurrentSku = DetachedCriteria.For<OrderItem>()
    .SetProjection(Projections.GroupProperty("Product.id"))
    .AddOrder(NHibernate.Criterion.Order.Desc(Projections.Count("Order.id")))
    .Add<OrderItem>(x=>x.Product.SKU!=sku)
    .Add(Subqueries.PropertyIn("Order.id", orderIDsContainingCurrentSku))
    .SetMaxResults(15);
var recommended = _session.CreateCriteria<Product>()
    .SetFetchMode<Product>(x => x.Descriptors, FetchMode.Join)
    .Add(Subqueries.PropertyIn("id", skusOfProductsAppearingInOrdersContainingCurrentSku))
    .SetResultTransformer(Transformers.DistinctRootEntity)
    .List<Product>();

这是结果SQL：

SELECT this_.SKU                 as SKU1_1_,
   this_.ProductName         as ProductN2_1_1_,
   this_.BasePrice           as BasePrice1_1_,
   this_.WeightInPounds      as WeightIn4_1_1_,
   this_.DateAvailable       as DateAvai5_1_1_,
   this_.EstimatedDelivery   as Estimate6_1_1_,
   this_.AllowBackOrder      as AllowBac7_1_1_,
   this_.IsTaxable           as IsTaxable1_1_,
   this_.DefaultImageFile    as DefaultI9_1_1_,
   this_.AmountOnHand        as AmountO10_1_1_,
   this_.AllowPreOrder       as AllowPr11_1_1_,
   this_.DeliveryMethodID    as Deliver12_1_1_,
   this_.InventoryStatusID   as Invento13_1_1_,
   descriptor2_.SKU          as SKU3_,
   descriptor2_.DescriptorID as Descript1_3_,
   descriptor2_.DescriptorID as Descript1_4_0_,
   descriptor2_.Title        as Title4_0_,
   descriptor2_.Body         as Body4_0_
FROM   Products this_
   left outer join ProductDescriptors descriptor2_
     on this_.SKU = descriptor2_.SKU
WHERE  this_.SKU in (SELECT   top 15 this_0_.SKU as y0_
FROM     OrderItems this_0_
WHERE    not (this_0_.SKU = 'Binoculars2' /* @p0 */)
    and this_0_.OrderID in (SELECT this_0_0_.OrderID as y0_
        FROM   OrderItems this_0_0_
        WHERE  this_0_0_.SKU = 'Binoculars2' /* @p1 */)
            GROUP BY this_0_.SKU
            ORDER BY count(this_0_.OrderID) desc)

请参阅http://ayende.com/blog/4315/building-a-recommendation-engine-in-nhibernate如何完成！

如何将这个HQL转换为DetachedCriteria？

2 个答案: