Is there a practical way of migrating from identity columns to hilo keys?

Question

I work with a database that depends heavily on identity columns. However as we have now moved all applications over to NHibernate I wanted to look into using HiLo as seems to be

Answer 1

I wrote a script (based of Stephans answer) for fixing hilo values (on sql server) - it assumes that you have a hilo table like

CREATE TABLE [dbo].[HiloValues](
    [next_hi] [int] NULL,
    [Entity] [varchar](128) NOT NULL
)

And your table's identity columns are all called ID. Init the Entity table with the table names you want to generate the hilo values for. Running the script will generate a series of update statements like this one:

UPDATE hv 
SET next_hi = Transactions.ID/(10 + 1) + 1 
FROM HiloValues hv 
CROSS JOIN (SELECT ISNULL(Max(ID), 0) as id FROM Transactions) as Transactions
WHERE hv.entity = 'Transactions'

Here it is

DECLARE @scripts TABLE(Script VARCHAR(MAX))
DECLARE @max_lo VARCHAR(MAX) = '10';

INSERT INTO @scripts
SELECT '
UPDATE hv 
SET next_hi = ' + Entity + '.ID/(' + @max_lo + ' + 1) + 1 
FROM HiloValues hv 
CROSS JOIN (SELECT ISNULL(Max(ID), 0) as id FROM ' + entity + ') as ' + entity + '
WHERE hv.entity = ''' + entity + '''' as script 
FROM HiloValues WHERE Entity IN (SELECT  name from sys.tables)



DECLARE curs CURSOR FOR SELECT * FROM @scripts
DECLARE @script VARCHAR(MAX)

OPEN curs 
FETCH NEXT FROM curs INTO @script

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT @script --OR EXEC(@script)
    FETCH NEXT FROM curs INTO @script
END
CLOSE curs
DEALLOCATE curs