[英]Entity Framework navigating using navigation properties more than one level
I have Entity model classes as follows 我有如下的实体模型类
public partial class User
{
public User()
{
this.webpages_Roles = new HashSet<webpages_Roles>();
}
public int UserID { get; set; }
public virtual ICollection<webpages_Roles> webpages_Roles { get; set; }
}
. 。
public partial class webpages_Roles
{
public webpages_Roles()
{
this.Users = new HashSet<User>();
this.Roles_X_ApplicationModules =
new HashSet<Roles_X_ApplicationModules>();
}
public int RoleId { get; set; }
public virtual ICollection<User> Users { get; set; }
public virtual ICollection<Roles_X_ApplicationModules>
Roles_X_ApplicationModules { get; set; }
}
. 。
public partial class Roles_X_ApplicationModules
{
public long ID { get; set; }
public Nullable<int> ModuleID { get; set; }
public Nullable<int> RoleID { get; set; }
public Nullable<bool> ViewPermission { get; set; }
public virtual ApplicationModule ApplicationModule { get; set; }
public virtual webpages_Roles webpages_Roles { get; set; }
}
.and 。和
public partial class ApplicationModule
{
public ApplicationModule()
{
this.Roles_X_ApplicationModules =
new HashSet<Roles_X_ApplicationModules>();
}
public int ModuleID { get; set; }
public virtual ICollection<Roles_X_ApplicationModules>
Roles_X_ApplicationModules { get; set; }
}
you can see User
object has a navigation property to webpages_Roles
which again has navigation property to Roles_X_ApplicationModules
and which in turn navigates to ApplicationModule
.. 您可以看到User
对象具有webpages_Roles
的导航属性,该对象又具有Roles_X_ApplicationModules
导航属性,然后又导航到ApplicationModule
。
now I want to get all the ApplicationModule from User..how do I write query using navigation properties.. 现在我想从用户那里获取所有ApplicationModule。如何使用导航属性编写查询。
I tried something like this.. 我尝试过这样的事情。
var appModules = user.webpages_Roles.SingleOrDefault()
.Roles_X_ApplicationModules.Where(z => z.ViewPermission == true)
.Select(x => x.ApplicationModule);
but problem with this is, it doesn't issue a single query to database. 但这是问题,它不会对数据库发出单个查询。 It splits the query to get the webpages_Roles
at SingleOrDefault
then another query to get the Roles_X_ApplicationModules
based on the RoleId
and at the end as many queries as Roles_X_ApplicationModules
matching the condition to get the ApplicationModule
. 它将该查询来获取webpages_Roles
在SingleOrDefault
然后另一个查询来获取Roles_X_ApplicationModules
基础上, RoleId
,并在年底尽可能多的查询, Roles_X_ApplicationModules
符合条件得到ApplicationModule
。
How do I write the LINQ query so that a single sql query is issued to database? 如何编写LINQ查询,以便向数据库发出单个sql查询?
You can use Include()
to do this. 您可以使用Include()
来执行此操作。 Example: 例:
card = Cards.Include(l => l.DocumentLinks)
.Include(l => l.Charges.Select(ch => ch.DocumentLinks)
.SingleOrDefault(c=>c.Id==id);
This is for three linked Entities: 这是针对三个链接的实体:
public class Card
{
public Guid Id{get;set;}
public virtual ICollection<DocumentLink> DocumentLinks{get;set;}
public virtual ICollection<Charge> Charges{get;set;}
}
public class Charge
{
...
public virtual ICollection<DocumentLink> DocumentLinks{get;set;}
}
public class DocumentLink
{
...
}
try this: 尝试这个:
var appModules = from u in user
from w in u.webpages_Roles
from am in w.Roles_X_ApplicationModules
where am.ViewPermission == true
select am;
if you want eager loading then you just need to call ToList: 如果您想快速加载,则只需致电ToList:
var appModules = (from u in user
from w in u.webpages_Roles
from am in w.Roles_X_ApplicationModules
where am.ViewPermission == true
select am).ToList();
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