foreign key with 'no foreign key' value - sql-server

Question

In my application I use MS SQL Server 2008 and Linq-to-SQL. I have two tables: A and B, linked with foreign key: B.AId => A.Id. Is it possible in B.AId to have a value, for instance -1, which means 'no A' and ignores foreign key?
I can't use NULL in B.AId because Linq-to-SQL does not correclty support one-to-oneorzero associations (unfortunately).

Answer 1

Created a sample model with tables A and B
CREATE TABLE [dbo].[A](
[Id] [int] NOT NULL,
[AA] [varchar](50) NOT NULL,
[AAA] [varchar](50) NOT NULL,
CONSTRAINT [PK_A] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
CREATE TABLE [dbo].[B](
[Id] [int] NOT NULL,
[BB] [varchar](50) NOT NULL,
[BBB] [varchar](50) NOT NULL,
[AId] [int] NULL,
CONSTRAINT [PK_B] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
ALTER TABLE [dbo].[B] WITH CHECK ADD CONSTRAINT [FK_B_A] FOREIGN KEY([AId])
REFERENCES [dbo].[A] ([Id])
GO
ALTER TABLE [dbo].[B] CHECK CONSTRAINT [FK_B_A]
GO
After that generated a model from database. Even though it is recognized as a 1 to many relationship a navigation property A is created for table B.
I created a test and created three different rows in table B
Using navigation property A
Using Id of A
Created a row without reference to A
using (var db = new DataClasses1DataContext())
{
// Add sample A row
var sampleARow = new A()
{
Id = 1,
AA = "AA",
AAA = "AAA",
};
db.As.InsertOnSubmit(sampleARow);
db.SubmitChanges();
// Refer to sample A row using navigation property
var sampleNewBRowWithNav = new B()
{
Id = 1,
BB = "BB1",
BBB = "BBB1",
A = db.As.First(),
};
// Refer to sample A row using Id
var sampleNewBRowWithId = new B()
{
Id = 2,
BB = "BB2",
BBB = "BBB2",
AId = 1,
};
// No reference to A
var sampleNewBRowWithoutA = new B()
{
Id = 3,
BB = "BB3",
BBB = "BBB3",
AId = null // strictly not needed, because AId is default null
};
db.Bs.InsertOnSubmit(sampleNewBRowWithNav);
db.Bs.InsertOnSubmit(sampleNewBRowWithId);
db.Bs.InsertOnSubmit(sampleNewBRowWithoutA);
db.SubmitChanges();
}