[Helma-user] allowing NULL VALUES in foreign keys

[Julian Tree]

I came from a heavily database oriented background working a lot with  
stored procedures, triggers, and foreign key constrains . I was told  
to NOT allow NULL values in any database columns, because it prevents  
the column from beingporperly  indexed.  I usually put a sentinel  
value for all columns, ['' for string, 0 for number], even for  
timestamps I use a sentinel value such as '0001-01-01 00:00:00' as a  
place holder.

I notice helma sets a foreign_key or any key to null if one of the  
parent is not set.  For example files has two paretns, Job and Company


Files/type.properties------------
_table = files
_id = files_id
file_name    		= file_Name

job 				= object(Job)
job.local   		= file_job_id
job.foreign 		= job_id

company			= object(Company)
company.local   		= file_company_id
company.foreign 		= company_id
-----------------------

//first add File to a job first and a few days later,  assign the  
file to a company
var f = new Files();
job.add(f);
// f._id = 123
/// this will insert NULL into file_company_id

How are everyone's handling NULL values on a foreign key? Is NOT NULL  
column really unindexable? or am I worrying over nothing.  I am using  
postgresql 8.1.x, BTW.

Julian