Re: How to store and represent 1 objects relationship to other objects
Daniele Futtorovic wrote:
pat.trainor@ allegedly wrote:
In other words and this maybe a database question, 1 of many
thousands of objects is related to any number of other objects. The
problem is how to represent or index those relationships each 1 being
perhaps either a parent, a child, or a peer of 1 or more thousands of
objects.
I have trouble understanding your question, especially why you pose it
in such an abstract manner.
It's your data you're talking about, right? Well, then you'd better know
If so, then that's bad. They should be talking about their object model.
darn well how they're related. Once you have established what those
relationships are, you map them. There ain't many candidates. You've got
many-to-one, one-to-many, unidirectional one-to-one and bidirectional
one-to-one relationships. That's about it.
Your starting point must be to analyse what you're modelling, methinks.
Yes, from an object-modeling standpoint.
A common mistake with JPA is to use it as a glorified JDBC, with a data-centric
approach. Its purpose is to provide an object-centric approach that maps to a
data store, not to replace relational modeling or even represent it.
So first question to analyze while modeling: what entities relate to what entities?
How do you model that relationship?
For example, if a retail order system models than an "Order" has multiple "Line Items"
for which reproducible order matters, you likely would have an object model that includes
public class Order
{
List<LineItem> lineItems;
...
}
If you further wish to guarantee that no 'LineItem' appears more than once, you'd likely use a 'Set'
instead of a 'List'. Unfortunately the JPA spec doesn't seem to allow 'SortedSet', but it seems that
the '@OrderBy' annotation hacks around that limitation.
--
Lew