NHibernate QueryOver投影多对一 [英] NHibernate QueryOver projection on many-to-one
问题描述
我正在尝试使用many-to-one上的投影来使QueryOver工作.
I am trying to get a QueryOver working using a Projection on a many-to-one.
"Post"类具有属性many-to-one"Creator".
The class "Post" has a property many-to-one "Creator".
使用
session.QueryOver(Of Post).
Select(Projections.
Property(of Post)(Function(x) x.Creator).
WithAlias(Function() postAlias.Creator)).
TransformUsing(Transformers.AliasToBean(Of Post)()).
List()
可以，但是每个创建者都可以通过单个查询来检索，而不是像不使用选择/投影时那样使用联接来检索.因此，如果有5个帖子由5个不同的创建者创建，则将针对帖子列表运行1个查询，对创建者运行5个查询.
works BUT each creator is retrieved by a single query rather than using a join like it is done when not using a select/projection. So if there are 5 posts with 5 different creators, 6 queries will be run 1 for the list of posts and 5 for the creators.
我尝试使用JoinAlias使其正常工作，但实际上没有任何作用.
I tried to get it working using a JoinAlias but nothing really did the job.
我已经在寻找解决方案，但是我发现的所有解决方案都使用了Linq-Provider，因为实际的字段列表"是通过参数传递的，所以它并不适合.
I already searched for a solution, but all solutions I found did use the Linq-Provider which does not really fit since the actual "field list" is passed via a parameter.
除了linq提供程序之外，还有谁知道解决方案吗?
Does anyone know if there is a solution to this other than the linq provider?
推荐答案
有一个解决方案，我们可以将 projections 用于many-to-one，然后使用自定义结果转换器.
There is a solution, we can use projections for many-to-one and then custom result transformer.
免责声明:我可以阅读VB语法，但没有足够的勇气来编写...我希望您可以阅读C#并将其转换为VB....
所以我们可以这样投影:
So we can have projection like this:
// aliases
Post root = null;
Creator creator = null;
// projection list
var columns = Projections.ProjectionList();
// root properties
columns.Add(Projections.Property(() => root.ID).As("ID"));
columns.Add(Projections.Property(() => root.Text).As("Text"));
// reference properties
columns.Add(Projections.Property(() => creator.ID).As("Creator.ID"));
columns.Add(Projections.Property(() => creator.FirstName).As("Creator.FirstName"));
// so our projections now do have proper ALIAS
// alias which is related to domain model
// (because "Creator.FirstName" will be use in reflection)
var query = session.QueryOver<Post>(() => root)
.JoinAlias(() => root.Creator, () => creator)
.Select(columns)
现在，我们需要智能的 Transformer ，这是我们自己的习惯(可插入性是NHibernate的强大功能).在这里您可以找到一个:
Now we would need smart Transformer, our own custome one (plugability is power of NHibernate). Here you can find one:
我们可以像这样继续
var list = query
.TransformUsing(new DeepTransformer<Post>())
.List<Post>()
还请检查以下内容:
- Fluent NHibernate - ProjectionList - ICriteria is returning null values
- NHibernate AliasToBean transformer associations
这篇关于NHibernate QueryOver投影多对一的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
