`:date` inflation returning a timestamp instead of a date

[daninus14]

When a :date col-type is inflated, a local-time timestamp is returned instead of either just the string value of the date or an object representing a date. See here:

mito/src/core/dao/column.lisp

Line 79 in c337a17

(:method ((col-type (eql :date)) value)

mito/src/core/dao/column.lisp

Line 86 in c337a17

(local-time:universal-to-timestamp

Note that deflation is fine because it allows for the string value:

mito/src/core/dao/column.lisp

Line 134 in c337a17

(:method ((col-type (eql :date)) value)

I would hope standard behavior for :date returns a date, whether as a string or an object, not a different data type.

Can we either return a string or at least use a date typed object?

There are a few libraries to deal with dates specifically, since local-time only deals with timestamps. See here: https://github.com/CodyReichert/awesome-cl?tab=readme-ov-file#date-and-time

Two in particular jumped to mind, both built on top of local-time:

• https://github.com/copyleft/calendar-times
• https://github.com/jwiegley/periods

It seems only periods is available in quicklisp: https://www.quicklisp.org/beta/releases.html

I would be happy to make a PR to fix this. I have no horse in choosing whichever library, I would just like for the dates to return a correct data type.

What do you think?

Originally posted by @daninus14 in #184

[daninus14]

Actually take it back, it looks like periods doesn't actually deal with dates. Just found the docs: https://lisp-maintainers.github.io/periods/#Fixed-time

The most basic element of time used by the PERIODS library is the fixed-time structure. At present, this is just a type alias for local-time structures2, so all of the operations possible on a local-time are applicable to a fixed-time.

So calendar-times seems like the only one who has date data types.

> (caltimes:parse-timestring "2025-11-24" 'caltimes:date)
#<CALENDAR-TIMES:DATE 2025-11-24>
> (caltimes:format-caltime nil (caltimes:parse-timestring "2025-11-24" 'caltimes:date))
"2025-11-24"

I just added an issue for it to be added to quicklisp: quicklisp/quicklisp-projects#2507

[daninus14]

Well, since calendar-times is not yet in quicklisp, not sure if this will get added until quicklisp updates.

I am sharing here my implementation for when it's needed so that we can make a PR

(defmethod mito.dao.column:inflate-for-col-type ((col-type (eql :date)) value)
  (etypecase value
    (integer
     (calendar-times:universal->date value))
    (string
     (calendar-times:parse-timestring value 'caltimes:date))
    (null nil)))

Note that I had to make some additions to calendar-times itself for the conversions. See here: copyleft/calendar-times#4

Hopefully that PR will have been merged by the time quicklisp adds the library.

[daninus14]

Update: The PR for calendar-times was accepted.

[daninus14]

Update: quicklisp added calendar-times for the next distribution. Whenever it's ready, I can make a PR. quicklisp/quicklisp-projects#2507 (comment)

Would you accept the PR? I know you don't like adding dependencies, which is a good thing. calendar-times is just a wrapper around local-time to deal with dates, since local-time is for timestamps.

[daninus14]

Update: calendar-times has been added to quicklisp: http://blog.quicklisp.org/2026/01/january-2026-quicklisp-dist-update-now.html