Custom columns and epub metadata

[xmodder]

Hi to all

I know that installing in Calibre the plugin Modify Epub, and checking the checkbox "Update Metadata (including cover)", you can update your ebooks in epub format with the metadata you have put on Calibre for that ebook. This not only updates standard metadata fields (as author, title and so on) on the file content.opf inside the epub, but also creates custom metadata fields on content.opf in the form:

<meta content="{&quot;is_category&quot;: true, &quot;is_editable&quot;: true, &quot;kind&quot;: &quot;field&quot;, &quot;is_custom&quot;: true, &quot;name&quot;: &quot;Hugo&quot;, &quot;#extra#&quot;: null, &quot;datatype&quot;: &quot;series&quot;, &quot;colnum&quot;: 3, &quot;rec_index&quot;: 22, &quot;search_terms&quot;: [&quot;#hugo&quot;], &quot;link_column&quot;: &quot;value&quot;, &quot;label&quot;: &quot;hugo&quot;, &quot;is_multiple&quot;: null, &quot;column&quot;: &quot;value&quot;, &quot;#value#&quot;: null, &quot;category_sort&quot;: &quot;value&quot;, &quot;table&quot;: &quot;custom_column_3&quot;, &quot;is_multiple2&quot;: {}, &quot;display&quot;: {}}" name="calibre:user_metadata:#hugo" />

Well, that was a simple custom column to indicate if a book has won an Hugo prize.

My question is if it is possible to do the reverse. I mean: Is it possible to recover this data from an epub to Calibre? Not thinking on creating automatically custom columns for that, (doing that would be a dream, but I understand that thecnically it seems hard to do) but, if I have a Calibre library that includes the same custom colums that correspond to that custom metadata fields in the content.opf file, is there a way to make Calibre to retrieve the values in the custom fields metadata into the corresponding custom columns? Simply matching by name, for example. And only for editable custom columns, calculated custom columns can be recreated on Calibre, but those data stored on custom columns would be lost if the book is exported.

As of now, I can't do that on Calibre... I have a book that includes the previous described custom metadata on the file content.opf, I have created a custom column with the same name on the calibre library, but neither when I add the book to the libray or update metada from the epub, that custom column is not populated with the content of the custom metadata in content.opf.

So, any idea on how to accomplish this?

[kovidgoyal]

The only time that calibre reads custom column metadata from OPF files is during a restore library operation, during which it will even re-create missing custom columns.

[capnm]

Restoring some books from a backup (don't ask), here's what I did:

Created a new, empty library.
Copied the book folders into the library folder, being careful to produce a valid library folder structure.
(Re)built the library with the restore database function.
Copied the books into the desired library with the copy to library function.

[xmodder]

Originally Posted by kovidgoyal

The only time that calibre reads custom column metadata from OPF files is during a restore library operation, during which it will even re-create missing custom columns.

Ok... I think I have finally understood that you are referring to the metadata.opf files present on each directory in a calibre libray. I was not referring to that OPF files, but to the content.opf file that each epub includes as part of the structure of the .epub file.

The metadadata.opf files created by calibre for each book in the library only contains metadata defined for the corresponding calibre library.
As you know, each .epub file contains a "content.opf" file inside, that holds metadata and the files manifest for the epub. That metadata contained in the internal content.opf file is the one I am interested in.

Calibre reads that metadata from internal epub content.opf file when adding books to a libray (if you have configured that in preferences , what is the default) but only reads standard metadata, not custom ones. Also calibre recovers stadard metadata from content.opf in .epub when you click the button "Import metadata from selected format", but again, only standard metadata, not custom ones.

So, my question is if there is some way to tell calibre to read not only standard metadata from that internal content.opf file but also custom metadata. Again, from the .epub internal content.opf file, not from the external, calibre created, metadata.opf.

Best regards

[theducks]

Originally Posted by xmodder

Ok... I think I have finally understood that you are referring to the metadata.opf files present on each directory in a calibre libray. I was not referring to that OPF files, but to the content.opf file that each epub includes as part of the structure of the .epub file.

The metadadata.opf files created by calibre for each book in the library only contains metadata defined for the corresponding calibre library.
As you know, each .epub file contains a "content.opf" file inside, that holds metadata and the files manifest for the epub. That metadata contained in the internal content.opf file is the one I am interested in.

Calibre reads that metadata from internal epub content.opf file when adding books to a libray (if you have configured that in preferences , what is the default) but only reads standard metadata, not custom ones. Also calibre recovers stadard metadata from content.opf in .epub when you click the button "Import metadata from selected format", but again, only standard metadata, not custom ones.

So, my question is if there is some way to tell calibre to read not only standard metadata from that internal content.opf file but also custom metadata. Again, from the .epub internal content.opf file, not from the external, calibre created, metadata.opf.

Best regards

Your EPUB may fail validation with 'non-standard fields error'

[xmodder]

Originally Posted by theducks

Your EPUB may fail validation with 'non-standard fields error'

I don't see why this should give any validation problem, custom metadata fields on epubs are contemplated on the epub specifications.

And, by the way, Fligthcrew doesn't complain about it. Just tested some epubs with custom metadata and check is OK.

[theducks]

You may be right about Flightcrew. I Know you can't SET a custom field using the Metadata editor of Sigil

[kovidgoyal]

No, there is no way to tell calibre to read custom column metadata from inside a book file.