c# - LINQ 查询获取具有指定类型成员的所有实体

Question

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“产品”为“预订”的所有订单的最佳方式是什么？当我使用以下查询时，我在 SQL 中得到一堆 CASE。

var query = from order in context.Orders
            where order.Product is Book
            select order.Product as Book;

更新 Aducci 的解决方案比我的好得多，但在更复杂的查询中我仍然会遇到重载的 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!

Answer 1

不确定生成的 SQL 是否会更好

var query = context.Orders.Select(order => order.Product).OfType<Book>();