我有以下实体和DbContext：
public class Customer
{
[Key]
public Guid Guid { get; set; }
[Required]
public string FullName { get; set; }
public virtual ICollection<Order> Orders { get; set; }
}
public abstract class Product
{
[Key]
public Guid Guid { get; set; }
[Required]
public String Title { get; set; }
}
public class Book : Product
{
public String Author { get; set; }
public String Year { get; set; }
}
public class DVD : Product
{
public String Genre { get; set; }
public String Country { get; set; }
public String MPAA { get; set; }
public String Year { get; set; }
}
public class Order
{
[Key, Column(Order = 0)]
public Guid CustomerGuid { get; set; }
[Key, Column(Order = 1)]
public Guid ProductGuid { get; set; }
public Int16 Quantity { get; set; }
public Decimal Price { get; set; }
public Decimal Total { get; set; }
public virtual Customer Customer { get; set; }
public virtual Product Product { get; set; }
}
public class StoreContext : DbContext
{
public DbSet<Customer> Customers { get; set; }
public DbSet<Book> Books { get; set; }
public DbSet<DVD> DVDs { get; set; }
public DbSet<Order> Orders { get; set; }
public StoreContext(string nameOrConnectionString)
: base(nameOrConnectionString)
{
}
}
查询Product is Book的所有订单的最佳方法是什么？当我使用以下查询时，我在SQL中获得了一堆CASE。
var query = from order in context.Orders
where order.Product is Book
select order.Product as Book;
更新的 Aducci的解决方案比我的好得多，但我仍然在更复杂的查询中得到重载SQL。
例如，
var query = context.SaleOffers.Select(x => x.Realty).OfType<Flat>().Select(x => x.Planning.Name);
SQL：
SELECT
[Extent10].[Name] AS [Name]
FROM [dbo].[SaleOffers] AS [Extent1]
INNER JOIN [dbo].[Offers] AS [Extent2] ON [Extent1].[Guid] = [Extent2].[Guid]
LEFT OUTER JOIN (SELECT [UnionAll5].[C1] AS [C1], [UnionAll5].[C2] AS [C2], [UnionAll5].[C3] AS [C3], [UnionAll5].[C4] AS [C4], [UnionAll5].[C5] AS [C5], [UnionAll5].[C6] AS [C6], [UnionAll5].[C7] AS [C7]
FROM (SELECT
[UnionAll4].[C1] AS [C1],
[UnionAll4].[C2] AS [C2],
[UnionAll4].[C3] AS [C3],
[UnionAll4].[C4] AS [C4],
[UnionAll4].[C5] AS [C5],
[UnionAll4].[C6] AS [C6],
[UnionAll4].[C7] AS [C7]
FROM (SELECT
[UnionAll3].[C1] AS [C1],
[UnionAll3].[C2] AS [C2],
[UnionAll3].[C3] AS [C3],
[UnionAll3].[C4] AS [C4],
[UnionAll3].[C5] AS [C5],
[UnionAll3].[C6] AS [C6],
[UnionAll3].[C7] AS [C7]
FROM (SELECT
[UnionAll2].[C1] AS [C1],
[UnionAll2].[C2] AS [C2],
[UnionAll2].[C3] AS [C3],
[UnionAll2].[C4] AS [C4],
[UnionAll2].[C5] AS [C5],
[UnionAll2].[C6] AS [C6],
[UnionAll2].[C7] AS [C7]
FROM (SELECT
[UnionAll1].[Guid] AS [C1],
[UnionAll1].[C1] AS [C2],
[UnionAll1].[C2] AS [C3],
[UnionAll1].[C3] AS [C4],
[UnionAll1].[C4] AS [C5],
[UnionAll1].[C5] AS [C6],
[UnionAll1].[C6] AS [C7]
FROM (SELECT
[Extent3].[Guid] AS [Guid],
CAST(NULL AS uniqueidentifier) AS [C1],
cast(0 as bit) AS [C2],
cast(0 as bit) AS [C3],
cast(0 as bit) AS [C4],
cast(0 as bit) AS [C5],
cast(0 as bit) AS [C6]
FROM [dbo].[Rooms] AS [Extent3]
UNION ALL
SELECT
[Extent4].[Guid] AS [Guid],
[Extent4].[PlanningGuid] AS [PlanningGuid],
cast(1 as bit) AS [C1],
cast(0 as bit) AS [C2],
cast(0 as bit) AS [C3],
cast(0 as bit) AS [C4],
cast(0 as bit) AS [C5]
FROM [dbo].[Flats] AS [Extent4]) AS [UnionAll1]
UNION ALL
SELECT
[Extent5].[Guid] AS [Guid],
CAST(NULL AS uniqueidentifier) AS [C1],
cast(0 as bit) AS [C2],
cast(1 as bit) AS [C3],
cast(0 as bit) AS [C4],
cast(0 as bit) AS [C5],
cast(0 as bit) AS [C6]
FROM [dbo].[CommercialProperties] AS [Extent5]) AS [UnionAll2]
UNION ALL
SELECT
[Extent6].[Guid] AS [Guid],
CAST(NULL AS uniqueidentifier) AS [C1],
cast(0 as bit) AS [C2],
cast(0 as bit) AS [C3],
cast(1 as bit) AS [C4],
cast(0 as bit) AS [C5],
cast(0 as bit) AS [C6]
FROM [dbo].[Houses] AS [Extent6]) AS [UnionAll3]
UNION ALL
SELECT
[Extent7].[Guid] AS [Guid],
CAST(NULL AS uniqueidentifier) AS [C1],
cast(0 as bit) AS [C2],
cast(0 as bit) AS [C3],
cast(0 as bit) AS [C4],
cast(1 as bit) AS [C5],
cast(0 as bit) AS [C6]
FROM [dbo].[Garages] AS [Extent7]) AS [UnionAll4]
UNION ALL
SELECT
[Extent8].[Guid] AS [Guid],
CAST(NULL AS uniqueidentifier) AS [C1],
cast(0 as bit) AS [C2],
cast(0 as bit) AS [C3],
cast(0 as bit) AS [C4],
cast(0 as bit) AS [C5],
cast(1 as bit) AS [C6]
FROM [dbo].[Lots] AS [Extent8]) AS [UnionAll5]
INNER JOIN [dbo].[Realties] AS [Extent9] ON [UnionAll5].[C1] = [Extent9].[Guid] ) AS [Join2] ON [Extent2].[RealtyGuid] = [Join2].[C1]
LEFT OUTER JOIN [dbo].[References] AS [Extent10] ON ([Extent10].[Discriminator] = 'FlatPlanning') AND ((CASE WHEN ([Join2].[C1] IS NULL) THEN CAST(NULL AS uniqueidentifier) WHEN ([Join2].[C4] = 1) THEN CAST(NULL AS uniqueidentifier) WHEN ([Join2].[C3] = 1) THEN [Join2].[C2] WHEN ([Join2].[C5] = 1) THEN CAST(NULL AS uniqueidentifier) WHEN ([Join2].[C6] = 1) THEN CAST(NULL AS uniqueidentifier) WHEN ([Join2].[C7] = 1) THEN CAST(NULL AS uniqueidentifier) END) = [Extent10].[Guid])
WHERE CASE WHEN ([Join2].[C1] IS NULL) THEN CAST(NULL AS varchar(1)) WHEN ([Join2].[C4] = 1) THEN '3X0X' WHEN ([Join2].[C3] = 1) THEN '3X1X' WHEN ([Join2].[C5] = 1) THEN '3X2X' WHEN ([Join2].[C6] = 1) THEN '3X3X' WHEN ([Join2].[C7] = 1) THEN '3X4X' ELSE '3X5X' END LIKE '3X1X%'
提前致谢！
答案 0 :(得分：5)
不确定生成的SQL是否会更好
var query = context.Orders.Select(order => order.Product).OfType<Book>();
答案 1 :(得分：0)
不能直接回答您的问题，但我想知道如果您向Product添加了类型鉴别器列，您是否会获得更好的SQL：
public abstract class Product
{
[Key]
public Guid Guid { get; set; }
[Required]
public String Title { get; set; }
public ProductType Type { get; set; }
}
然后您可以在查询中使用它，并且可能会避免加载不属于特定类型的产品。
答案 2 :(得分：0)
在使用某些继承模型时，我在生成的TSQL中看到了这种讨厌。我通过使用EntitySQL而不是LINQ
来修复类似的东西SELECT VALUE b
FROM OFTYPE(MyNs.Products, MyNs.Book)
AS b
EF短暂使用了由于某种原因使用eSQL OFTYPE运算符时使用LINQ.OfType创建的嵌套子选项。 （另见http://msdn.microsoft.com/en-us/library/bb399295.aspx#Y639）