Re: Stepping Back: A Wealth Of Completion systems Re: [ELPA] New package: vertico

[Jean Louis <bugs@gnu.support>]

* Philip Kaludercic <philipk@posteo.net> [2021-04-11 14:19]:
> 
> Dmitry Gutov <dgutov@yandex.ru> writes:
> 
> > - It uses data structures quite different from what completing-read
> >   uses. That's pretty inconvenient, and requires a mental switch. I'd 
> > rather the two functions (or some future versions of them) were more
> > similar in shape, yet (obviously) different in behavior.
> 
> I think it would be possible to also support alists, hash tables,
> vectors but I'm not sure if it is necessary. Functions might be
> interesting to consider.

Helm has good support for such data structures. Completing-read can
also support hashes. I would like that such functions support variety
of data structures. Because they don't I have to cope with
it. Currently I am removing the built-in helm from all my functions as
I want them to work with any completion system.

One way I use for complex data structures is to have some kind of ID
and visual description, then by using the ID I fetch the data
structure later.

(defun rcd-completing-read-sql-hash (prompt sql pg &optional history initial-input)
  "Complete selection by using SQL.

First column shall be unique id, followed by text representation. Example SQL query:

SELECT people_id, people_firstname || ' ' || people_lastname FROM people

PG is database handle. HISTORY is supported with INITIAL-INPUT"
  (let* ((hash (rcd-sql-hash-with-key sql pg))
	 (values (hash-table-values hash))
	 (length (length values)))
    (if (= length 1)
	  (car values)
      (let* ((completion-ignore-case t)
	     (choice (completing-read prompt hash nil t initial-input history))
	     (choice (string-trim choice))
	     (id (gethash choice hash)))
	id))))

(defun rcd-sql-hash-with-key (sql pg)
  "Returns hash with key TEXT [ID] and value ID from SQL result
in the form ID, TEXT"
  (let ((hash (make-hash-table :test 'equal))
	(res (rcd-sql sql pg)))
    (dolist (i res hash)
      (cond ((eq (type-of i) 'vector) (puthash (format "%s [%s]" (elt i 1) (elt i 0)) (elt i 0) hash))))))

Then I can complete by using database entries which are converted to
hash. And I place unique IDs appended to the string such as:

Selection entry [123]

Some entries may have duplicate names. Showing the ID is necessary to
make the name unique as selection time.


-- 
Jean

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