Question

我一直在阅读和探讨以黑白的方式找到答案。

Let s talk about the familiar Customer and Order problem. Let s say I load 100 orders, and each order is linked to one and only one customer.

Using Fluent NHibernate, I will use References() to link my Order to Customer and I will define my Not.LazyLoad() and Fetch.Join() as well.

Now I am thinking hypothetically, NHibernate can simply join these two tables and would be pretty easy to hydrate entities. However, in my tests I always see rather N+1 queries (in fact perhaps only the unique IDs). I can share my code and tables but it might bore you, so

Is it possible to overcome N+1 for Order->Customer (one->one or rather Many->One)? Or I have to use batching or Criteria API?
If possible can you please point me to an Fluent NHibernate example?

Answer 1

经常有人抱怨说,fetch=“join”没有工作。这是因为《刑法》没有考虑这一问题。您可在总部所在地宣布。

我使用了fetch=“join”,希望提高业绩,但在许多情况下停止使用。问题在于,加入许多表格可使服务器进入列栏上限。在某些情况下,你根本不需要数据,因此,在全球制图档案中说明数据并不有用。

因此,我建议

either use explicit join fetching in HQL, because there you know if the data is actually used.
or for any other case, batches are a great solution, because they are transparent (your code doesn t need to know about), make use of lazy loading and reducing the N+1 problem at the same time.

Answer 2

我只想看一下你正在做的实际询问。我把我的所有地图都留给了拉齐·洛德,否则就会落空。

I use the Criteria API to query, and I use CreateAlias to join other tables as needed. NHProf is highly recommended to find and eliminate situations like this.

Answer 3

Hi
There are two ways you can address your problem

a) Using Criteria query It will look something like this

Session.CreateQuery(typeof(Order))
.Add(<Restrictions if any>)
.SetFetchMode("Customer",FetchMode.Eager)
.List<Order>();

b) 使用总部

Session.CreateQuery("select o from Order inner join fetch o.Customer where <conditionifany>").List<Order>();

希望。

Answer 4

您使用了什么样的预报?

如果是“波尔图”,你可以使用<代码>join fetch,急切检索一个协会。

LINQ和QueryOver使用.Fetch(

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