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Re: [IndexedDB] IDBCursor.update for cursors returned from IDBIndex.openCursor

From: Jeremy Orlow <jorlow@chromium.org>
Date: Thu, 16 Sep 2010 10:15:25 +0100
Message-ID: <AANLkTimcWfNvj+xXS01qrzWrhaR5Yhc3qK5ue3DJ5uRK@mail.gmail.com>
To: Jonas Sicking <jonas@sicking.cc>
Cc: public-webapps WG <public-webapps@w3.org>
On Wed, Sep 15, 2010 at 10:45 PM, Jonas Sicking <jonas@sicking.cc> wrote:

> Heh, I've also been thinking about this exact issue lately. There is a
> similar question for IDBCursor.delete.
>
> On Wed, Sep 15, 2010 at 8:55 AM, Jeremy Orlow <jorlow@chromium.org> wrote:
> > I think it's clear what IDBCursor does when created from
> > IDBObjectStore.openCursor or IDBIndex.openObjectCursor: it modifies the
> > objectStore's value and updates all indexes (or does nothing and returns
> an
> > error if all of that can't be done while satisfying the constraints).
>
> Agreed.
>
> > But what about IDBCursor.update when created from IDBIndex.openCursor?  I
> > see two options: we could modify the value within the objectStore's value
> > that corresponds to the objectStore's key path or we could do like above
> and
> > simply modify the objectStore's value.
>
> There's also a third option: Throw an exception. Maybe that's what
> you're referring to by "make this unsupported" below?
>
> > More concretely, if we have an object store with a "id" key path and an
> > index with a "fname" key path, and our index.openCursor() created cursor
> is
> > currently on the {id: 22, fname: "Fred"} value (and thus cursor.key ==
> > "Fred" and cursor.value == 22), let's say I wanted to change the object
> to
> > be {id: 23, fname: "Fred"}.  In other words, I want id to change from 22
> to
> > 23.  Which of the following should I write?
> > 1) calling cursor.update(23)   or
> > 2) calling cursor.update({id: 23, fname: "Fred"})
> > The former seems to match the behavior of the IDBObjectStore.openCursor
> and
> > IDBIndex.openObjectCursor better (i.e. it modifies the cursor.value).
>  The
> > latter intuitively seems like it'd be more useful.  But to be honest, I
> > can't think of any use cases for either.  Can anyone else?  If not, maybe
> we
> > should just make this unsupported for now?
>
> The only use case I have thought of is wanting to update some set of
> entries, where the best way to find these entries is through an index.
> For example updating every entry with a specific shipping-id. You can
> use IDBIndex.openObjectCursor for this, but that's slower than
> IDBIndex.openCursor. So in the rare instance when you can make the
> modification without inspecting the existing value (i.e. you only need
> to write, read-modify-write), then IDBIndex.openCursor +
> IDBCursor.update() would be a perf optimization.
>
> On the other hand, it might be just as quick to call IDBObjectStore.put().
>
> Since the use case if pretty weak (when would you be able to update an
> entry without first reading the entry), and that you can seemingly get
> the same performance using IDBObjectStore.put(), I would be fine with
> making this unsupported.
>
> As for IDBCursor.delete(), I can see a somewhat stronger use case
> there. For example removing all entries with a specific shipping-id or
> some such. If you can determine which entries should be removed purely
> on the information in the index, then using IDBIndex.openCursor is
> definitely faster than IDBIndex.openObjectCursor. So on one hand it
> would be nice to allow people to use that. On the other hand, I
> suspect you can get the same performance using IDBObjectStore.delete()
> and we might want to be consistent with IDBCursor.update().
>
> In this case I'm actually leaning towards allowing IDBCursor.delete(),
> but I could go either way.
>

Wait a sec.  What are the use cases for non-object cursors anyway?  They
made perfect sense back when we allowed explicit index management, but now
they kind of seem like a premature optimization or possibly even dead
weight.  Maybe we should just remove them altogether?

J
Received on Thursday, 16 September 2010 09:16:16 GMT

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