var result = from x in _context.Bunts
                             select x;

SELECT 
"A"."BUNTCODE" AS "BUNTCODE", 
"A"."BUNTNAME" AS "BUNTNAME", 
"A"."BUNTDIAM" AS "BUNTDIAM"
FROM "BUNTS" AS "A"

[Table("BUNTS")]
    public class Bunt
    {
        [Key]
        [Column("BUNTCODE")]
        public int Code { set; get; }
        [Column("BUNTNAME")]
        public string Name { set; get; }
        [Column("BUNTDIAM")]
        public double? Diametr { set; get; }
    }

Database.SetInitializer<EFDbContext>(null);