nhibernate - 急切获取引用时重复(多对一)

Question

首先，是的，我使用的是 DistinctRootEntityResultTransformer。

我有以下(Fluent NHibernate)映射:

public FirstObjectMap() 
{
    Id(x => x.Id):
    HasMany<SecondObject>(x => x.SecondItems).KeyColumn("FirstObject_ID");
}

public SecondObjectMap()
{
    Id(x => x.Id).Column("ID");
    References(x => x.ThirdObject).Column("ThirdObject_ID");
}

public ThirdObjectMap()
{
    Id(x => x.Id).Column("ID");
    HasMany<D>(x => x.FourthItems).KeyColumn("ThirdObject_ID");
}

public FourthObjectMap()
{
    Id(x => x.Id).Column("ID");
}

注意，SecondObject 指的是 ThirdObject(意思是键在 SecondObject 上)。

我的查询如下所示:

var query = session.CreateQuery("select distinct first from " + 
   "FirstObject as first " +
   "left join fetch first.SecondItems as second " +
   "left join fetch second.ThirdObject as third " + 
   "left join fetch third.FourthItems as four where ...");

// This is not even needed as I'm using distinct in HQL
query.SetResultTransformer(new DistinctRootEntityResultTransformer());

var results = query.List<ReinsurableObject>();

为了进行测试，我在数据库中有 1 个 FirstObject、1 个 SecondObject、1 个 ThirdObject 和 24 个 FifthObject。 SQL 查询按预期返回 24 行。

然而，这里有一个问题:NHibernate 创建:

1 FirstObject
  24 SecondObject (should be 1)
     24 x 1 ThirdObject (should be 1)
         24 x 1 x 24 FourthObject (should be 24)

因此，无论出于何种原因，NH 都会创建 24 SecondObject 而不是 1。

我猜它不知道如何将“join fetch”(左或内部似乎无关紧要)映射到 Reference(对 SecondObject 中的 ThirdObject 的引用)。

我有哪些选择？我无法更改数据模型，但我确实需要急切加载它。

提前致谢!

Answer 1

不同的根实体仅在您加载父级和子级时才有效。对于孙辈和曾孙辈来说，这是行不通的。问题是您正在加载多个集合关联并返回一个大 cartesian product
请阅读此 article by Ayende这解释了为什么会出现这种情况和解决方法。

Something that may not be apparent immediately is going to result in a Cartesian product. This is pointed out in the documentation, but I think that we can all agree that while there may be reasons for this behavior, it is far from ideal.