NHibernate：使用子集合的子集获取多个实体？
我的类看起来像这样（我只包含相关属性）：
public class Order
{
public virtual Customer Customer { get; set; }
public virtual IEnumerable<OrderLine> OrderLines { get; set; }
}
public class OrderLine
{
public virtual string Product { get; set; } // Simplified
}
现在我想要的是创建一个独立的条件，选择给定客户的所有订单，同时仅检索每个订单的前 10 个 OrderLine。第一部分很简单：
Customer someCustomerObject = ...;
var criteria = DetachedCriteria.For<Order>().Add(Restrictions.Eq("Customer", someCustomerObject);
但是我如何指示 NHibernate 为按上述条件检索的每个订单急切地检索前 10 个订单行？
我尝试使用基于以下示例的过滤器（取自 Nhibernate 文档）：
session.CreateFilter( lazyCollection, "").SetFirstResult(0).SetMaxResults(10).List();
但是当我将 Order.OrderLines 赋予 CreateFilter 方法时，它首先检索所有订单行，然后检索前 10 个订单行，这不是我想要的。我还尝试将其与对 NHibernateUtil.Initialize 的调用结合起来，但无济于事。
如何为这个问题创建一个独立的标准？或者，如果这不完全可能，如何为每个订单仅检索前 10 个结果，而不获取整个集合？
My classes look something like this (I include only the relevant properties):
public class Order
{
public virtual Customer Customer { get; set; }
public virtual IEnumerable<OrderLine> OrderLines { get; set; }
}
public class OrderLine
{
public virtual string Product { get; set; } // Simplified
}
Now I What I want is to create a detached criteria that selects all orders for a given customer, and at the same time retrieves only the first 10 OrderLines for each order. The first part is easy:
Customer someCustomerObject = ...;
var criteria = DetachedCriteria.For<Order>().Add(Restrictions.Eq("Customer", someCustomerObject);
But how do I instruct NHibernate to retrieve eagerly the first 10 orderlines for each order retrieved by the criteria above?
I've tried using a Filter based on the following example (taken from Nhibernate documentation):
session.CreateFilter( lazyCollection, "").SetFirstResult(0).SetMaxResults(10).List();
But when I give Order.OrderLines to the CreateFilter method, it retrieves all orderlines first, and then afterwards retrieves the 10 first orderlines, which is not what I want. I also tried combining this with a call to NHibernateUtil.Initialize to no avail.
How do I create a detached criteria for this problem? Or, if that is not entirely possible, how to I retrieve, for each order, the 10 first results only, without fetching the entire collection?
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您可以在 Order 类的 NHibernate 映射文件中将
batch-size属性设置为 10。这样，它会急切地加载集合的前 10 个元素，并延迟加载其余元素。我将按如下方式映射该集合：更多信息，请阅读：NHibernate 映射 - 集合
You can set the
batch-sizeproperty to 10 in the NHibernate mapping file for the Order class. This way it eagerly loads the first 10 elements of the collection and lazy-loads the rest of elements. I would map the collection as follows:More information, read on: NHibernate Mapping - Collections