CREATE TABLE [dbo].[Shape](
	[Id] [int] IDENTITY( 1 , 1 ) NOT NULL PRIMARY KEY,
	[ShapeCode] [nvarchar]( 2 ) COLLATE SQL_Latin1_General_CP1251_CI_AS NULL,
	[StartingX] [int] NULL,
	[StartingY] [int] NULL,
	[Length] [int] NULL,
	[Width] [int] NULL
)

[Table]
[InheritanceMapping(Code = "G", Type = typeof(Shape), IsDefault = true)]
[InheritanceMapping(Code = "S", Type = typeof(Square))]
public class Shape
{
[Column(IsPrimaryKey = true, IsDbGenerated = true,
DbType = "Int NOT NULL IDENTITY")]
public int Id;
[Column(IsDiscriminator = true, DbType = "NVarChar(2)")]
public string ShapeCode;
[Column(DbType = "Int")]
public int StartingX;
[Column(DbType = "Int")]
public int StartingY;
}
public class Square : Shape
{
[Column(DbType = "Int")]
public int Width;
}

dataGridView1.DataSource =
                from c in db.GetTable <Shape>()
                where c is Square
                select c;

  dataGridView1.AutoGenerateColumns = true;
  dataGridView1.DataSource = from c in db.GetTable<Shape>()
                                            where c is Square
                                            select c; 

 dataGridView1.DataSource = from c in db.GetTable<Square>()                                            
                                            select c; 

 dataGridView1.DataSource = from c in db.GetTable<Shape>()
                                            where c is Square
                                            select c as Square;

var q = db.Vehicle.Where(p => p is Truck);
foreach (Truck p in q)
   Console.WriteLine(p.Axles);

exec sp_executesql N'SELECT [t0].[Key], [t0].[Tonnage], [t0].[Axles], [t0].[VIN], [t0].[MfgPlant]
FROM [Vehicle] AS [t0]
WHERE ([t0].[Key] = @p0) AND ([t0].[Key] IS NOT NULL)',N'@p0 nvarchar(1)',@p0=N'T'

var query = from p in ctx.GetTable<Person>()
            select p; 

foreach (Person p in query)
{
    if ( p is Employee )
        // Do something with employees
}

    [Table(Name = "dbo.StrRefer")]
    [InheritanceMapping(Code = "G", Type = typeof(StrRefer), IsDefault = true)]
    [InheritanceMapping(Code = "Упаковки", Type = typeof(Packs))]
    public class StrRefer
    {
        [Column(IsDiscriminator = true, DbType = "NVarChar(64)")]
        public string str_code { get; set; }
        [Column]
        public string str_value { get; set; }

    }
    //str_value
    public class Packs : StrRefer
    {

    }

   var q=    from c in db.GetTable<StrRefer>()
                where c is Packs
                select c; // ТО что надо!