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Re: How to store and represent 1 objects relationship to other objects

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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

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How to store and represent 1 objects relationship to other objects pat.trainor@gmail.com - 2012-10-26 11:40 -0700
  Re: How to store and represent 1 objects relationship to other objects Lew <lewbloch@gmail.com> - 2012-10-26 12:23 -0700
  Re: How to store and represent 1 objects relationship to other objects Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-10-26 22:59 +0200
    Re: How to store and represent 1 objects relationship to other objects Lew <lewbloch@gmail.com> - 2012-10-26 14:51 -0700
      Re: How to store and represent 1 objects relationship to other objects Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-10-27 00:48 +0200
        Re: How to store and represent 1 objects relationship to other objects Lew <lewbloch@gmail.com> - 2012-10-26 16:07 -0700
      Re: How to store and represent 1 objects relationship to other objects Gene Wirchenko <genew@ocis.net> - 2012-10-28 20:47 -0700
        Re: How to store and represent 1 objects relationship to other objects David Lamb <dalamb@cs.queensu.ca> - 2012-10-29 10:12 -0400

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