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Re: [EP-tech] Virtual fields -when does the 'cost' of processing get triggered?

CAUTION: This e-mail originated outside the University of Southampton.

Hi,
Seems like no one knew- so I went down the investigation route.

 

For a virtual field, the 'cost' of the field occurs when te value is asked for, not when the EPrint object is instantiated.

 

This is a script I used to investigate:
https://gist.github.com/jesusbagpuss/553234bf241caf4d3aab78d0c5b3066c

 

It steps through a few basic questions (archive id, eprintid, field to dump), but also allows you to set the 'noise' of the EPrints session.

This is the same mechanism that running  e.g.  ~/bin/epadmin --verbose --verbose --verbose uses.

 

Setting the noise to 3 will show SQL statements used when creating the EPrint object, or getting a field value.

 

It's not the most useful script as-is, but might be a useful base for other investigations.

 

Cheers,

John

 

 

From: eprints-tech-bounces@ecs.soton.ac.uk [mailto:eprints-tech-bounces@ecs.soton.ac.uk] On Behalf Of John Salter via Eprints-tech
Sent: 01 December 2022 09:06
To: 'eprints-tech@ecs.soton.ac.uk' <eprints-tech@ecs.soton.ac.uk>
Subject: [EP-tech] Virtual fields -when does the 'cost' of processing get triggered?

 

CAUTION: This e-mail originated outside the University of Southampton.

Hi All,

I'm looking adding a 'virtualwithvalue' (https://bazaar.eprints.org/452/1/plugins/EPrints/MetaField/Virtualwithvalue.pm) field to my EPrints install that does a search of the EPrint history, finding the first record, and returning the datestamp for that history item (i.e. the date the EPrint was created).

https://gist.github.com/jesusbagpuss/8b899eb0eb9b2b733eead25c6dfd5973

 

I was thinking about the processing overhead for this field, and wondered when the value is actually calculated. I guess it's one of these options:
- when the object is created in memory e.g. via an EPrints::DataObj::EPrint->new() call
- when the value is referenced e.g. $eprint->value( "virtualwithvalue_field" ) ;

 

If it's the first option, I should add the field to the EPrint dataobj as a non-virtual field, and calculate it once if the value is not set, and then store it.

If it's the second option, then the overhead is lower (although I might still want to do the above).

 

I could trace this through the system myself - but thought (hoped) that someone might know… J

 

Cheers,

John

 

John Salter

https://orcid.org/0000-0002-8611-8266

 

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