Fields that are not returned in Library/Fields endpoint, but are returned using Library/Search:
Key
Date (readable)
These are not actual library fields, but inserted by MCWS.
The key is of course the FileKey, and taken again as input for many MCWS calls, and Date (readable) is a pre-formatted variant of date.
The following fields are returned in Library/Fields with DataType "Date", but they are not JRiver Date formats (Numbers are far to big) - possibly classical timestamps? This causes automatic conversion to fail.
Date Imported
Date Created
Date Modified
Date First Rated
Date Tagged
Last Skipped
Last Played
Date Last Opened
We have two date types, Date (float) and Date.
Date (float) is a double-precision floating-point value in days since 1900. Its typically formatted to not include zero components, ie. if the resulting date falls on january 1st at midnight, it would only show the year. (if zero is supposed to be shown, there is a fudge factor of 1/10th of a second to make it not exactly zero - the magic of floating points!). Can also be negative for dates before 1900.
The Date type is a typical unix timestamp, with all its restrictions.
Currently, only the fields "Date", "Date (release)" and "Date Recorded" (not sure why it was chosen for this field, but we can't change it after) use the Date (float) type. The other Date fields are more closely related to actual interactions with the file or physical file properties, and use a unix timestamp.
The field list returned by the API should correctly reflect which field uses which date type.
Finally, to completely overstretch any goodwill: Would it be possible to also get the remaining properties of fields from that endpoint? Most relevant for me would be "acceptable values", but there's also:
I can add acceptable values, not sure how useful many of the other properties are.