Storing key-value metadata (for books, and for a whole library)

[isarl]

Suppose I have lots of key-value metadata that I wish to store for one or more books in my library. I do not know in advance what the keys will be, and there may be many of them, hundreds or thousands. The keys are small (word-sized) strings, and the values are integers.

Is there a better way of storing this information than as JSON-encoded data in a long-text (like comments) column?

Suppose further that I wish to store a similar set of key-value data, scoped to my whole library (or possibly one virtual library), rather than any one particular book. Does the Calibre plugin API offer any way of storing metadata for a library, instead of for a single book?

Thank you in advance.

[kovidgoyal]

use set_pref with a namespace of your plugin import name, to store library wide metadata.

There is no facility for storing per book key/value metadata with arbitrary key sets other than identifiers. But you probably shouldn't overload those as that is likely to affect performance in many places. You can simply create a new table in the sqlite database (use a unique table name) or use a custom column storing the key values serialized to text.

[chaley]

Depending on what you want to do book-by-book, the API db.cache.(add_custom_book_data(), get_custom_book_data(), delete_custom_book_data(), and get_ids_for_custom_book_data()) might do the job. These let you store and retrieve more-or-less arbitrary data on a book-by-book basis. Internally calibre uses a table with three columns (book_id, data_name, data_val), where data_val is the json representation of the data.

You could store a python dict of your key:value pairs.

If needed, you could give users access to the data via Python stored templates. The template would load the dict and return the desired value(s).

[kovidgoyal]

Yes add_custom_data might work, I forgot about that

[isarl]

This is SO helpful! Thank you very much Charles and Kovid!