No way to use TSQL Output with normal foreign key constraints?

Question

Following snippet fails with error, "The target table 'dbo.forn' of the OUTPUT INTO clause cannot be on either side of a (primary key, foreign key) relationship. Found reference constraint 'FK_forn_prim'."
I can only use output by disabling foreign key constraints? Surely I'm missing something...

IF OBJECT_ID ('dbo.forn') IS NOT NULL
begin
    alter table dbo.forn drop constraint FK_forn_prim
    DROP TABLE dbo.forn;
end
IF OBJECT_ID ('dbo.prim') IS NOT NULL
    DROP TABLE dbo.prim;
go

CREATE TABLE dbo.prim (c1 int PRIMARY KEY);
CREATE TABLE dbo.forn (c1 int CONSTRAINT FK_forn_prim FOREIGN KEY (c1) REFERENCES dbo.prim(c1));
go

INSERT INTO dbo.prim
    OUTPUT inserted.c1 INTO dbo.forn
SELECT 1;

Answer 1

According to technet

There is no guarantee that the order in which the changes are applied to the table and the order in which the rows are inserted into the output table or table variable will correspond.

Based on this there are a number of restrictions, among which is the one you ran into above, but if all you want is to record the inserted value in a second table I don't see why you would need the foreign key relationship you define above.

If you do need the foreign key relationship you could accomplish the same thing by using a trigger like this.

    IF OBJECT_ID ('dbo.forn') IS NOT NULL
begin
    alter table dbo.forn drop constraint FK_forn_prim
    DROP TABLE dbo.forn;
end
IF OBJECT_ID ('dbo.prim') IS NOT NULL
    DROP TABLE dbo.prim;
go

CREATE TABLE dbo.prim (c1 int PRIMARY KEY);
CREATE TABLE dbo.forn (c1 int CONSTRAINT FK_forn_prim FOREIGN KEY (c1) REFERENCES dbo.prim(c1));
go

CREATE TRIGGER InsertRecord
   ON  dbo.Prim
   AFTER Insert
AS 
BEGIN
    SET NOCOUNT ON;
    Insert into dbo.forn Select * from inserted;
END
GO

INSERT INTO dbo.prim SELECT 1;

Answer 2

Normally you output to a table variable or temp table, then use that to insert to the final table.