Entity Framework 6 TPH Inheritance Enum Field Generate Slow Query - performance

Question

I use EF 6.0 code first and TPH inheritance in my project. I see that if i use enum field in my classes EF generates sql statement with casting. So my query runs very slowly and performance is down. How can i remove casting in my sql query?
Thanks.
var db = new AppContext();
var p = db.Products.FirstOrDefault(x => x.ProdId == 1);
public enum MyEnum
{
Field1 = 1,
Field2 = 2
}
public class Product
{
[Key]
public int ProdId { get; set; }
public string ProdName { get; set; }
//I run my code with this property and without this property.
//public MyEnum MyEnum { get; set; }
}
public class Chair : Product
{
public string ChairProp1 { get; set; }
}
public class Seat : Product
{
public string SeatProp1 { get; set; }
}
//EF generate this SQL without enum field. This is good SQL statements.
SELECT TOP (1)
[Extent1].[Discriminator] AS [Discriminator],
[Extent1].[ProdId] AS [ProdId],
[Extent1].[ProdName] AS [ProdName],
[Extent1].[ChairProp1] AS [ChairProp1],
[Extent1].[SeatProp1] AS [SeatProp1]
FROM [dbo].[Products] AS [Extent1]
WHERE ([Extent1].[Discriminator] IN (N'Chair',N'Seat',N'Product')) AND (1 = [Extent1].[ProdId])
//EF generate this SQL with enum field (myenum). there is alot of casting.i want to remove casting.
SELECT
[Limit1].[C1] AS [C1],
[Limit1].[ProdId] AS [ProdId],
[Limit1].[ProdName] AS [ProdName],
[Limit1].[MyEnum] AS [MyEnum],
[Limit1].[C2] AS [C2],
[Limit1].[C3] AS [C3]
FROM ( SELECT TOP (1)
[Extent1].[ProdId] AS [ProdId],
[Extent1].[ProdName] AS [ProdName],
[Extent1].[MyEnum] AS [MyEnum],
CASE WHEN ([Extent1].[Discriminator] = N'Product') THEN '0X' WHEN ([Extent1].[Discriminator] = N'Chair') THEN '0X0X' ELSE '0X1X' END AS [C1],
CASE WHEN ([Extent1].[Discriminator] = N'Product') THEN CAST(NULL AS varchar(1)) WHEN ([Extent1].[Discriminator] = N'Chair') THEN [Extent1].[ChairProp1] END AS [C2],
CASE WHEN ([Extent1].[Discriminator] = N'Product') THEN CAST(NULL AS varchar(1)) WHEN ([Extent1].[Discriminator] = N'Chair') THEN CAST(NULL AS varchar(1)) ELSE [Extent1].[SeatProp1] END AS [C3]
FROM [dbo].[Products] AS [Extent1]
WHERE ([Extent1].[Discriminator] IN (N'Chair',N'Seat',N'Product')) AND (1 = [Extent1].[ProdId])
) AS [Limit1]

Answer 1

It seems you missed the configuration of discriminator . You need to specify which field is the discriminator and what's the type of that ,
You can do it by fluent api like this :
public class ChairConfig : EntityTypeConfiguration<Chair>
{
public ChairConfig()
{
this.Map(m => m.Requires(discriminator: "MyEnum").HasValue(MyEnum.Field1));
}
}
public class SeatConfig : EntityTypeConfiguration<Seat>
{
public SeatConfig()
{
this.Map(m => m.Requires(discriminator: "MyEnum").HasValue(MyEnum.Field2));
}
}
And in query you need to specify which type you wanna retrieve like this :
var db = new AppContext();
var p = db.Products.OfType<Chair>().FirstOrDefault(x => x.ProdId == 1);