Nhibernate QueryOver JoinAlias UnRelated Entity

问题描述

 <$>我在NHibernate中遇到了关于使用JoinAlias的左连接的问题。 c $ c>select * from EntityA T1 left join join EntityB T2 on T2.EntityAId = T1.id
  

$ $ $ $ $ $ $ $ $ $ var query = _session.QueryOver（（）=> EntityA）
.Left.JoinAlias（（）=> EntityA，（）=> EntityB.EntityA）

在NHibernate中 c 或 QueryOver 是不可能的。但是，我们可以使用 HQL ，它支持

• （小引用和片段）

 来自公式，参数
来自公式形式，参数为参数
  

所以在上面的例子中我们会有这样的HQL：

  FROM EntityA T1 
，EntityB T2 
 WHEERE T2.EntityAId = T1.id 
  

几乎是

但是在上面描述的情况下，存在着已经映射的反转关系。这意味着，我们可以扩展C＃实体定义：

  public class EntityA 
 {
 public int Id {get; set;} 
 //一对多
 //以下关系的双向映射
 public IList< EntityB> EntityBColl {get;组; } 
} 
 
 public class EntityB 
 {
 public int Id {get; set;} 
 //多对一
 //这是实际上双向映射的反转端
 public EntityA EntityA {get; set;} 
} 
  

具备这个功能，我们可以使用标准的 QueryOver API：

  //别名
 EntityA EntityA = null; 
 EntityB EntityB = null; 
 
 // query 
 var query = session.QueryOver（（）=> EntityA）
 .Left.JoinAlias（（）=&EntityA.EntityBColl，（）= >实体B）
 ... 
; 
  

I have an issue in NHibernate regarding a left join using "JoinAlias" when the result query SQL that I am looking for is this :

"select * from EntityA T1 left join EntityB T2 on T2.EntityAId=T1.id"

And in NHibernate I have this but doesn't work:

 var query = _session.QueryOver(() => EntityA)
                      .Left.JoinAlias(() => EntityA, () => EntityB.EntityA)

In NHibernate EntityA doesn't reference to EntityB but EntityB as a reference to EntityA.

public class EntityA
{ 
   public int Id {get;set;}
}

public class EntityB
{ 
   public int Id {get;set;}
   public EntityA EntityA {get;set;}
}

How can I make this very simple left join in HHibernate Work?

解决方案

This is not possible with Criteria or QueryOver. But we can use HQL, which does support that

• 14.2. The from clause (small cite and snippet)

from Formula, Parameter
from Formula as form, Parameter as param

So in the case above we would have HQL like this:

FROM EntityA T1 
   , EntityB T2 
WHEERE T2.EntityAId = T1.id

Almost the same issue

But in case described above, there is reversed relation, already mapped. And that means, that we can extend the C# entity definitions:

public class EntityA
{ 
   public int Id {get;set;}
   // one-to-many
   // the bidirectional mapping of the below relation
   public IList<EntityB> EntityBColl { get; set; }
}

public class EntityB
{ 
   public int Id {get;set;}
   // many-to-one
   // this is the inversed end in fact of the bidirectional mapping
   public EntityA EntityA {get;set;}
}

Having that in place, we can use standard QueryOver API:

// aliases
EntityA EntityA = null;
EntityB EntityB = null;

// query
var query = session.QueryOver(() => EntityA)
    .Left.JoinAlias(() => EntityA.EntityBColl , () => EntityB)
    ...
    ;

这篇关于Nhibernate QueryOver JoinAlias UnRelated Entity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！