Inserting records in database tables using "inheritance" - sql-server

Question

I have a table whose primary key is also a foreign key to the primary key of another table (i.e. "inheritance" as simulated in a database).
/****** Object: Table [dbo].[BaseClass] Script Date: 07/15/2011 18:17:27 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[BaseClass](
[ID] [int] IDENTITY(1,1) NOT NULL,
[Title] [nvarchar](50) NOT NULL,
[Description] [nvarchar](max) NOT NULL,
CONSTRAINT [PK_BaseClass] 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]
GO
USE [TestConcepts]
GO
/****** Object: Table [dbo].[DerivedTable] Script Date: 07/15/2011 18:17:49 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[DerivedTable](
[ID] [int] IDENTITY(1,1) NOT NULL,
[SpecialProperty] [uniqueidentifier] NOT NULL,
CONSTRAINT [PK_DerivedTable] 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]
GO
ALTER TABLE [dbo].[DerivedTable] WITH CHECK ADD CONSTRAINT [FK_DerivedTable_BaseClass] FOREIGN KEY([ID])
REFERENCES [dbo].[BaseClass] ([ID])
GO
ALTER TABLE [dbo].[DerivedTable] CHECK CONSTRAINT [FK_DerivedTable_BaseClass]
GO
What is the proper way to insert records in this situation? Obviously an insert doesn't return the PK of the inserted row (plus the child's table's PK is identity as well).

Answer 1

Here are a few examples of this pattern.
The sub-type table should not have auto-increment ID, the ID matches the one in the super-type table.
The basic technique (using your example) looks something like
DECLARE #MY_ID integer;
INSERT INTO BaseTable(Title, Description)
VALUES ('title_here', 'blah, blah');
SELECT #MY_ID = SCOPE_IDENTITY();
INSERT INTO DerivedTable(ID, SpecialProperty)
VALUES (#MY_ID, newid()); -- the SpecialProperty is uniqueidentifier
One approach is to create a view, one for each sub-type table, or just one over all of them. Then create an INSTEAD OF INSERT TRIGGER on the view and use the technique inside the trigger.
You may also find this technique for capturing multiple inserted IDs useful too.

Answer 2

Nobody calls this "inheritance". That's not what it is. It's a relation, the R in RDBMS.
INSERTs do tell you the PK of the just-inserted row. Look at ##SCOPE_IDENTITY on SQL Server.

Answer 3

The DERIVEDCLASS table could have an auto-incremented (identity) PK but if so there must be another column that is a foreign key reference back to BASETABLE:
BASETABLE
id int pk autoincrement
baseattribute1
baseattribute2
etc etc
DERIVEDTABLE
id int pk autoincrement
**baseid** foreign key references BASETABLE(id)
extendedattribute1
extendedattribute2
This would permit multiple derivations of each base entity. Placing a unique index on DERIVEDTABLE.baseid or making baseid the PK would prevent this, if that is desired.
The following would instantiate the members of the base class and their derived instances and/or extended properties if any [which it is will depend on whether baseid has unique constraint in DerivedTable; if the latter it could be the PK in a one-to-one relationship with BaseTable, rather than a many-to-one]:
select * from BASETABLE
LEFT JOIN DERIVEDTABLE
on BASETABLE.id = DERIVEDTABLE.baseid
Instances of the base class that have not been extended will have NULL in the extendedattribute columns.
To find only those entities that have been extended use an inner join:
select * from DERIVEDTABLE
inner join BASETABLE
on DERIVEDTABLE.baseid = BASETABLE.id