[ Bcc www-tag ; Marc - please use public-webapps for IDB discussions ]
On 5/20/14 7:46 PM, marc fawzi wrote:
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
