Question

我有以下实体：

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class HappyUser : User
{
    public bool IsHappy { get; set; }
}

我正在使用Table Per Concrete Type（TPC）配置实体，以生成User表和HappyUser表。我希望HappyUser表包含User类的属性，我不希望这两个表之间有任何关系。

我按如下方式配置实体：

public class UserTest : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<HappyUser> HappyUsers { get; set; }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<HappyUser>().Map(m =>
        {
            m.MapInheritedProperties();
            m.ToTable("HappyUser");
        });
    }
}

表是正确生成的，但是当我查询表时，EF会在User和HappyUser表上生成UNION。查询如下：

        UserTest db = new UserTest();

        var users = from u in db.Users
                    select u;

        var happyUsers = from u in db.Users.OfType<HappyUser>()
                         select u;

用户的SQL生成UNION。这不是我期望或想要的。我想简单地从Users表中检索行。

SELECT 
CASE WHEN ([UnionAll1].[C2] = 1) THEN '0X' ELSE '0X0X' END AS [C1], 
[UnionAll1].[Id] AS [C2], 
[UnionAll1].[Name] AS [C3], 
CASE WHEN ([UnionAll1].[C2] = 1) THEN CAST(NULL AS bit) ELSE [UnionAll1].[C1] END AS [C4]
FROM  (SELECT 
 [Extent1].[Id] AS [Id], 
 [Extent1].[Name] AS [Name], 
 CAST(NULL AS bit) AS [C1], 
 cast(1 as bit) AS [C2]
 FROM [dbo].[User] AS [Extent1]
UNION ALL
 SELECT 
 [Extent2].[Id] AS [Id], 
 [Extent2].[Name] AS [Name], 
 [Extent2].[IsHappy] AS [IsHappy], 
 cast(0 as bit) AS [C1]
 FROM [dbo].[HappyUser] AS [Extent2]) AS [UnionAll1]

HappyUsers的SQL按预期工作。

SELECT 
'0X0X' AS [C1], 
[Extent1].[Id] AS [Id], 
[Extent1].[Name] AS [Name], 
[Extent1].[IsHappy] AS [IsHappy]
FROM [dbo].[HappyUser] AS [Extent1]

任何想法我做错了什么？或者这是EF的缺陷？

Answer 1

HappyUsers 是用户。因此，db.Users 应返回两者。 EF在这里是正确的。

然而，EF确实有一个限制：无法（在L2E中，无论如何）返回仅一种类型的结果。由于Liskov Substitution Principal，您通常不想这样做。但如果你这样做，you can do it in ESQL, and there are (somewhat tedious) workarounds for L2E。

结论：如果您发现自己想要这样做，请重新考虑您的设计。在这种情况下，继承可能不是正确的关系。

Answer 2

@Craig Stuntz是对的，因为两种类型都是相关的，EF将保持这种关系不变。

如果要解耦两种用户类型，则可以使用抽象基类。

public abstract class AbstractUser
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class User : AbstractUser
{
}

public class HappyUser : AbstractUser
{
    public bool IsHappy { get; set; }
}

EF现在将两个实体分开处理，不再需要调用MapInheritedProperties()。

您的选择语句将如下所示：

var users = db.Users.Where(...);
var happyUsers = db.HappyUsers.Where(...);

EF Linq to实体查询为TPC CTP5代码优先实体生成UNION

2 个答案: