在nHibernate关系中使用Lite版本的实体？ [英] Using Lite Version of Entity in nHibernate Relations?

问题描述

在某些情况下创建一个实体的更轻版本是一个好主意，只是出于性能原因指向同一个表，但映射的列较少。例如，如果我有一个有50列的联系表，并且在少数相关实体中，我可能对FirstName和LastName属性感兴趣，那么创建Contact表的轻量版本是个不错的主意。例如，

  public class ContactLite 
 {
 public int Id {get; set;} 
 public string FirstName {get; set;} 
 public string LastName {get; set;} 
 
} 
  

也可以将多个类映射到同样的表？

解决方案

这不是一个好主意。相反，总是映射完整的类并创建可以使用 Transformers.AliasToBean 或LINQ进行投影的小类。

后一个例子：

  var lightContacts =（来自session.Linq中的联系人< Contact>（）
 where contact.Country =Argentina
选择新的LightContact 
 {
 Id = contact.Id 
 FirstName = contact.FirstName，
 LastName = contact.LastName 
}）
 .ToList（）; 
  

这将只从数据库中选择这三个字段，即使是用不同的字段过滤也是如此。 p>

值得注意的是，对于LINQ，您还可以使用匿名类型来选择您想要的任何投影，而无需创建其他类型或映射。

Is it a good idea to create a lighter version of an Entity in some cases just for performance reason pointing to same table but with fewer columns mapped. E.g If I have a Contact Table which has 50 Columns and in few of the related entities I might be interested in FirstName and LastName property is it a good idea to create a lightweight version of Contact table. E.g.

public class ContactLite
{
   public int Id {get; set;}
   public string FirstName {get; set;}
   public string LastName {get; set;}

}

Also is it possible to map multiple classes to same table?

解决方案

It's not a good idea. Instead, always map the full class and create smaller ones that you can project on using Transformers.AliasToBean or LINQ.

An example of the latter:

var lightContacts = (from contact in session.Linq<Contact>()
                     where contact.Country = "Argentina"
                     select new LightContact
                            {
                                Id = contact.Id
                                FirstName = contact.FirstName,
                                LastName = contact.LastName
                            })
                    .ToList();

This will only select those three fields from the DB, even when filtering by a different one.

It's worth noting that, with LINQ, you could also use an anonymous type to select any projection you want without creating additional types or mappings.

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