我需要使用Entity Framework(代码优先)列出所有订单及其相应的客户ID。这可以在不查询Customers表的情况下实现,因为客户ID是Orders表中的FK。但是,EF也会针对Orders和Customers表生成选择。
这是实体模型和用于查询订单的代码:
public class Order
{
public virtual Guid Id { get; set; }
public virtual string Description { get; set; }
public virtual Customer Customer { get; set; }
}
public class Customer
{
public virtual Guid Id { get; set; }
public virtual string Name { get; set; }
}
using (var context = new LazyLoadingEfContext())
{
foreach (var order in context.Orders)
{
Console.WriteLine("Order {0}, Customer {1}", order.Description, order.Customer.Id);
}
}
生成的SQL如下:
SELECT
1 AS [C1],
[Extent1].[Id] AS [Id],
[Extent1].[Description] AS [Description],
[Extent1].[Customer_Id] AS [Customer_Id]
FROM [dbo].[Orders] AS [Extent1]
exec sp_executesql N'SELECT
[Extent2].[Id] AS [Id],
[Extent2].[Name] AS [Name]
FROM [dbo].[Orders] AS [Extent1]
INNER JOIN [dbo].[Customers] AS [Extent2] ON [Extent1].[Customer_Id] = [Extent2].[Id]
WHERE ([Extent1].[Customer_Id] IS NOT NULL) AND ([Extent1].[Id] =
@EntityKeyValue1)',N'@EntityKeyValue1 uniqueidentifier',
@EntityKeyValue1='FF947EF3-5A3F-4A26-BDB9-039C49F559A7'
(加上参数@ EntityKeyValue1具有不同值的其他相同查询)
有没有办法配置EF以便从“父”对象中检索相关实体ID而不是加载相关实体?
BTW,我使用NHibernate测试了相同的场景,并且只对Orders表执行了一个查询:
SELECT this_.Id as Id1_0_, this_.Description as Descript2_1_0_,
this_.Customer_id as Customer3_1_0_ FROM [Order] this_
答案 0 :(得分:2)
试试这个:
public class Order
{
public virtual Guid Id { get; set; }
public virtual string Description { get; set; }
public Guid CustomerID { get; set; }
[ForeignKey("CustomerID ")]
public virtual Customer Customer { get; set; }
}
之后,您应该能够在order.CustomerID
循环中获得foreach
,而无需查询Customers表。