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I was always being told stop being so persistant...

 
Dave Brown
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G'day all,

Please can someone give me a one or two liner on, what does database persistanc e actually mean...

I am guessing an object setup with some OR mapping technology like hibernate can be 'live' so whenever something changes its automatically updated in a db or am I way off...

Thanks..

Dave.
 
Pj Murray
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Taken from a data perspective:


Persistant data are data that exists from session to session.

Persistent data are stored in some format that makes it available for later use: a database, a hard drive, a tape, a CD, etc.

In contrast, transient data is created within an application session but is discarded (or reset to default) at the end of the session.

So database persistence is simply another way of saying "storing data in a database".

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Of course, there's another related topic - Object persistence - and object - relational mapping. You may find this blog entry on Choosing a Java Persistence Strategy useful:

http://www.codefutures.com/weblog/andygrove/archives/2005/01/choosing_a_java.html

Hope this helps...
 
Dave Brown
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Thanks for that, good reply and helpfull blog entry.

I think what really started confusing me was a 'quick start' quide I found on hibernate that started mentioning that objects can be persisted or serialized.

Rgds,

Dave.
 
Pj Murray
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Object persistence is related, but rather different in approach, to data persistence.

Object persistence can be defined in a number of ways (and there's related topics such as BMP).

In the context that I think you are asking, I means the ability to store and retrieve objects within a database.

For many Java programmers, it's natural to start with objects and then to persist them. Of course, that could create problems (for example, if the database already exists). Then you run into the object-relational mapping problem.

Of course, many programmers start with the data model (new or pre-existing), then create the objects.
 
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