a curiosity about custom columns and opf

ZioNemo · 01-29-2014, 06:41 PM

I noticed that adding custom columns (or even simply shuffling columns around) will add a whole bunch of tags to each and all .opf and to data dumped via "calibredb show_metadata #".
The data seems to contain info about caolums and way of displaying them.
Added data also destroys opf formatting, but that's another story.
I was wondering why it is so.
I would have expected to have some metadata if (and only if) the column is filled for the specific book, displaying shouldn't be in the book metadata.
Obviously I'm looking at this from the wrong angle.
Can someone enlighten me?
TiA

Adoby · 01-29-2014, 08:05 PM

The opf-files can be used to reconstruct a calibre library with a missing or corrupt database. They are collectively a backup for metadata.db. Individually they are a backup of a record in metadata.db.

DoctorOhh · 01-30-2014, 01:38 AM

Quote:

Originally Posted by ZioNemo

I was wondering why it is so.

Assuming you're referring to the metadata.opf files in each book's directory then as Adobe points out they are a fail safe in case of metadata.db corruption. Having these files allows calibre, if needed, to reconstruct the metadata.db file. They have nothing to do with actual book files.

ZioNemo · 01-30-2014, 03:29 AM

Got it, thanks.
I assume You're using the same code to output "calibredb show_metadata --as-opf ##" and thus that info appears also there (where it doesn't really belong, does it?)
It makes .opf very hard to read, partially because xml formatting gets messed.
Thanks

Adoby · 01-30-2014, 07:31 AM

What information belongs in a opf-file?

The basic information like the one that is stored in calibre, without any custom columns, would perhaps be reasonable?

But then opf-files wouldn't have any purpose for epub books. They can store all(?) that information internally.

For other formats the opf-file is necessary if you want to move a book from one calibre install to another. A lot of the basic information about a book can't be stored as metadata inside many formats.

Yes, for some purposes some opf-files may contain a lot of unnecessary information. Perhaps there should be some setting that allow you to select exactly what to store in the opf-file. But you would have to think up a compelling use case where that would be needed. Until then we have to live with opf-files that store as much information as possible. That is what makes the opf-files suitable as backup of metadata.db. Or manually create a opf-file with just the needed information.

01-29-2014, 06:41 PM	#1
ZioNemo Enthusiast Posts: 48 Karma: 10 Join Date: Mar 2008 Device: HTC-p3000	a curiosity about custom columns and opf I noticed that adding custom columns (or even simply shuffling columns around) will add a whole bunch of tags to each and all .opf and to data dumped via "calibredb show_metadata #". The data seems to contain info about caolums and way of displaying them. Added data also destroys opf formatting, but that's another story. I was wondering why it is so. I would have expected to have some metadata if (and only if) the column is filled for the specific book, displaying shouldn't be in the book metadata. Obviously I'm looking at this from the wrong angle. Can someone enlighten me? TiA

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01-29-2014, 08:05 PM	#2
Adoby Handy Elephant Posts: 1,737 Karma: 26785684 Join Date: Dec 2009 Location: Southern Sweden, far out in the quiet woods Device: Samsung Galaxy Tab S8 Ultra	The opf-files can be used to reconstruct a calibre library with a missing or corrupt database. They are collectively a backup for metadata.db. Individually they are a backup of a record in metadata.db.

01-30-2014, 03:29 AM	#4
ZioNemo Enthusiast Posts: 48 Karma: 10 Join Date: Mar 2008 Device: HTC-p3000	Got it, thanks. I assume You're using the same code to output "calibredb show_metadata --as-opf ##" and thus that info appears also there (where it doesn't really belong, does it?) It makes .opf very hard to read, partially because xml formatting gets messed. Thanks

01-30-2014, 07:31 AM	#5
Adoby Handy Elephant Posts: 1,737 Karma: 26785684 Join Date: Dec 2009 Location: Southern Sweden, far out in the quiet woods Device: Samsung Galaxy Tab S8 Ultra	What information belongs in a opf-file? The basic information like the one that is stored in calibre, without any custom columns, would perhaps be reasonable? But then opf-files wouldn't have any purpose for epub books. They can store all(?) that information internally. For other formats the opf-file is necessary if you want to move a book from one calibre install to another. A lot of the basic information about a book can't be stored as metadata inside many formats. Yes, for some purposes some opf-files may contain a lot of unnecessary information. Perhaps there should be some setting that allow you to select exactly what to store in the opf-file. But you would have to think up a compelling use case where that would be needed. Until then we have to live with opf-files that store as much information as possible. That is what makes the opf-files suitable as backup of metadata.db. Or manually create a opf-file with just the needed information.

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