Re: Determine which child table a record belongs to

[Craig L Russell]

On Jan 29, 2008, at 10:49 AM, MZ_TRICSTA wrote:

tables, so that one instance has more than one "Type"?

One last question, guys. What if there is overlapping between the child

Craig

Then you might want to model this as an Entity-Role relationship which allows multiple rows in associated tables for the same row in the primary table. If this is the case, then you can't use a single-valued discriminator. You could use a bit field represented as a number in which each bit corresponds to an associated Role with data in another table.

Craig L Russell wrote:

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.


performance-limiting.

Craig Russell

This is a very common pattern in object-relational mapping. The column The alternative is to include all possible tables in a query, which is Architect, Sun Java Enterprise System http://java.sun.com/products/ jdo

408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
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