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IndexedDB >> Proposed API Change: cursor.advance BACKWARD when direction is "prev"

From: marc fawzi <marc.fawzi@gmail.com>
Date: Tue, 20 May 2014 16:46:02 -0700
Message-ID: <CACioZivk2HNqJRO4=rJzNSBowZazidcYgSYB3Tc6mcH=+rbGFg@mail.gmail.com>
To: www-tag@w3.org
Hi everyone,

I've been using IndexedDB for a week or so and I've noticed that
cursor.advance(n) will always move n items forward regardless of cursor
direction. In other words, when the cursor direction is set to "prev" as
in: range = IDBKeyRange.only(someValue, "prev") and primary key is
auto-incremented, the cursor, upon cursor.advance(n), will actually advance
n items in the opposite direction to the cursor.continue() operation. This
is not only an issue of "broken symmetry" but it presents an obstacle to
doing things like: keeping a record of the primaryKey of the last found
item (after calling cursor.continue for say 200 times) and, long after the
transaction has ended, call our search function again and, upon finding the
same item it found first last time, advance the cursor to the previously
recorded primary key and call cursor.continue 200 times, from that offset,
and repeat whenever you need to fetch the next 200 matching items. Such
algorithm works in the forward direction (from oldest to newest item)
because cursor.advance(n) can be used to position the cursor forward at the
previously recorded primary key (of last found item) but it does not work
in the backward direction (from newest to oldest item) because there is no
way to make the cursor advance backward. It only advances forward,
regardless of its own set direction.

This example is very rough and arbitrary. But it appears to me that the
cursor.advance needs to obey the cursor's own direction setting. It's
almost like having a car that only moves forward (and can't u-turn) and in
order to move backward you have to reverse the road. That's bonkers.

What's up with that?

How naive or terribly misguided am I being?

Thanks in advance.

Marc
Received on Wednesday, 21 May 2014 13:54:44 UTC

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