How to set up validate rule to check a query that the serial number does not exist

Have a table form for data entry and one of the fields is to enter the serial number.  Want to use the validation rule to check a query (need the query cause want it to check only records not annotated as closed for the serial number existence).  Do not want to allow the user to enter a serial number that already exist on a record not annotated as closed (which is a checkbox field in the record of the table).  Am using the query as the closed field is in the order hdr table and the serial number is in the order line table.
HFSCIAsked:
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Rey Obrero (Capricorn1)Connect With a Mentor Commented:
use the beforeUpdate event of the textbox for serial

private sub txtserial_beforeUpdate(cancel as integer)

if dcount("*","Open serial","serial='" & me.txtserial &"'")>0 then
   msgbox "Serial already exists!"
end if


end sub
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PatHartmanConnect With a Mentor Commented:
You can't do this with a validation rule.  You will need to do it with code in the BeforeUpdate event of the control on the form.

If Dcount("*", "yourtable", "Closed = False") > 0 Then
    Msgbox "This serial number already exists.  Please enter another.",vbokOnly
    Cancel = True
    Exit Sub
End If

Open in new window


If you want to clear the serial number, add:
Me.txtSerialNum.undo
between Cancel and Exit.

I rarely erase something that the user has typed.  It is usually better for them to see what they typed so they can correct it rather than forcing them to enter the entire value again.  This is particularly relevant with long number strings.

If you have a SQL Server BE  you can create a trigger that will perform this validation.  Since the trigger is applied at the table level, it is a much more robust solution because it will be enforced regardless of where the update request comes from.  Using form events means that your business rule will only be applied if you do the update via that particular form.  A2010+ (and possibly A2007 but I'm not sure) support data macros which are similar to triggers.  I don't know if they have the ability to run queries but you could look into it.
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HFSCIAuthor Commented:
don't think I made myself clear so have attached a doc showing the info.  Thanks
Serial-Validation.doc
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