Question

We got a script to disable FK constraints by passing ‘D’ deactivate ‘A’ for activate.
Once these are disabled, they get enabled back again after couple of hours or a day.
What could be the reason ?

Script is as below:

CREATE PROCEDURE [dbo].[sp_DisableEnableForeignKeys] @PutFK CHAR(1)
as

 DECLARE @IdFK integer
 DECLARE @ForeignKey sysname
 DECLARE @ChildTable sysname
 DECLARE @ParentTable sysname
 DECLARE @ParentColumn sysname
 DECLARE @ChildColumn sysname
 DECLARE @ParentColumns varchar(1000)
  DECLARE @ChildColumns varchar(1000)



    IF EXISTS (SELECT 1 FROM sysobjects where type = 'U' and Name ='metForeignKeys')
        DROP TABLE metForeignKeys


    SELECT * INTO metForeignKeys FROM 
    (
    SELECT 
        FK.constid as IdFK,
        FK.KeyNo,
        sofk.name as [Foreign Key Name],
        soch.name as [Child Table],
        scch.name as [Child Column],
        sopa.name as [Parent Table],
        scpa.name as [Parent Column]
    FROM 
        sysforeignkeys FK

    INNER JOIN sysobjects sofk on FK.constId = sofk.id
    INNER JOIN sysobjects soch on FK.fkeyid = soch.id
    INNER JOIN syscolumns scch on FK.fkeyid = scch.id and FK.fkey = scch.colid
    INNER JOIN sysobjects sopa on FK.rkeyid = sopa.id
    INNER JOIN syscolumns scpa on FK.rkeyid = scpa.id and FK.rkey = scpa.colid
    )T  


    DECLARE met_C_Delete CURSOR FOR SELECT DISTINCT IdFK, [Child Table] FROM metForeignKeys ORDER BY [Child Table]
    OPEN met_C_Delete

    FETCH NEXT FROM met_C_Delete into @IdFK, @ChildTable
    WHILE @@Fetch_Status = 0
    BEGIN
        SELECT @ForeignKey = [Foreign Key Name], @ChildTable = [Child Table], @ParentTable = [Parent Table] 
            FROM metForeignKeys where IdFK = @IdFK

        IF @PutFK = 'D'
        BEGIN
            EXEC( 'ALTER TABLE [' + @ChildTable + '] with check nocheck constraint ' + @ForeignKey)

                IF @@ERROR = 0
                    BEGIN
                        --PRINT 'Disabled FK Constraint ' + @ForeignKey + ' on table ' + @ChildTable + ' referencing '+@ParentTable
                        PRINT @ChildTable+' - Disabled FK Constraint ' + @ForeignKey + ' referencing '+@ParentTable
                    END
                ELSE
                    BEGIN
                        PRINT 'Error disabling FK Constraint ' + @ForeignKey + ' on table ' + @ChildTable + ' referencing '+@ParentTable
                        --PRINT @ChildTable+' - Enabled FK Constraint ' + @ForeignKey + ' referencing '+@ParentTable
                    END
                END
        ELSE
            BEGIN
                EXEC( 'ALTER TABLE [' + @ChildTable + '] with check check constraint ' + @ForeignKey)
                IF @@ERROR = 0
                    BEGIN
                        PRINT 'Enabled FK Constraint ' + @ForeignKey + ' on table ' + @ChildTable + ' referencing '+@ParentTable
                    END
                ELSE
                    BEGIN
                        PRINT 'Error enabling FK Constraint ' + @ForeignKey + ' on table ' + @ChildTable + ' referencing '+@ParentTable
                    END
            END

        FETCH NEXT FROM met_C_Delete into @IdFK, @ChildTable
    END

    CLOSE met_C_Delete
    DEALLOCATE met_C_Delete

Answer 1

A foreign key will not reenable itself automatically on an out-of-the-box SQL Server installation.

Perhaps a DBA was worried that developers would forget to reenable constraints (a common problem!) and wrote a job to periodically reenable any disabled constraints?

If you are having trouble tracking this down, you could define a DDL trigger on the database to log the times and user names of all modifications (ALTER_TABLE event).