db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From MZ_TRICSTA <mz_tric...@yahoo.com>
Subject Re: Determine which child table a record belongs to
Date Tue, 29 Jan 2008 18:49:34 GMT

One last question, guys. What if there is overlapping between the child
tables, so that one instance has more than one "Type"?

Craig L Russell wrote:
> This is a very common pattern in object-relational mapping. The column  
> that contains the type of crane is commonly referred to as a  
> discriminator column, and is commonly a CHAR, VARCHAR, or NUMERIC  
> type. The value of the discriminator column that identifies which  
> table to look for is referred to as a discriminator value.
> The alternative is to include all possible tables in a query, which is  
> performance-limiting.
> Craig Russell
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
View this message in context: http://www.nabble.com/Determine-which-child-table-a-record-belongs-to-tp15164998p15166419.html
Sent from the Apache Derby Users mailing list archive at Nabble.com.

View raw message