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From cbeams <cbe...@gmail.com>
Subject Re: JDO 2.1 spec draft: designing default values for convenience in annotations
Date Wed, 08 Aug 2007 23:59:11 GMT
Having used the annotations in their evolving forms for the last  
several months, I and my fellow developers have gotten very used to  

     @Persistent(persistenceModifier = PERSISTENT, defaultFetchGroup  
= "true")
     private MyObject obj;

To the uninitiated, it seems rather redundant to be using an  
annotation named "@Persistent", and then have to pass in "PERSISTENT"  
again.  It would be nice if this were the default, and in the (in my  
experience) much less frequent cases of TRANSIENT/UNKNOWN/NONE, I'm  
free to configure away.

The same goes for defaultFetchGroup.  Granted, I'm building an  
application that relies heavily on detachment, thus I want everything  
in my DFG, but from an ease-of-use / reducing the learning-curve  
point of view, I'd like to consider introducing 'reasonable defaults'  
into the annotations, such that I can type

     private MyObject obj;

and it will 'just work', whether I'm attached / detached, etc.  As I  
begin to optimize, and want to take things out of my DFG, I can  
configure that easily enough by passing defaultFetchGroup = "false",  
but at that point, I must care about it enough to figure it out,  
right?  (refer to hype in general about convention over  
configuration :-)

While I'm on the topic, would it be unreasonable to make the  
'detachable' parameter to @PersistenceCapable default to "true"?  If  
this has performance implications (i.e.: extra bytecode has to get  
added during enhancement for objects that are detachable vs those  
that aren't), perhaps an option could be introduced to advise the  
implementation whether detachable is "true" or "false" by default.  I  
know for me, every single one of my calls to @PersistenceCapable  
includes a 'detachable="true"'.  This just feels punitive after a while.

I haven't given a great deal of thought to these suggested changes  
and their possible ramifications, but perhaps that's the benefit of  
being an 'ignorant user'... I just know what I want from a  
convenience and ease-of-use point of view.  That said, one  
implication I can think of is that the annotations' default behavior  
would no longer map directly to that of the already-established XML  
metadata.  The second paragraph of the preamble to chapter 19 would  
have to change to accommodate this.  It currently reads:

	The annotations described herein support the entire range of  
metadata that can be expressed using the xml format. Annotations have  
identical semantics to the corresponding xml metadata.

The semantics might be the same, but the defaults would be changing.   
We would want to account for this in the spec, I'm sure.

Food for thought, thanks much.

- Chris

Chris Beams
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