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Re: [Bug 11257] New: Should IDBCursor.update be able to create a new entry?

From: Jonas Sicking <jonas@sicking.cc>
Date: Thu, 11 Nov 2010 22:26:57 -0800
Message-ID: <AANLkTi=dJdXW96VNQ_OxLnsZf6k-pCQvAXZQq6dBgz-=@mail.gmail.com>
To: Jeremy Orlow <jorlow@chromium.org>
Cc: public-webapps@w3.org
On Thu, Nov 11, 2010 at 9:12 PM, Jeremy Orlow <jorlow@chromium.org> wrote:
> On Fri, Nov 12, 2010 at 12:11 AM, Jonas Sicking <jonas@sicking.cc> wrote:
>>
>> On Thu, Nov 11, 2010 at 11:51 AM, Jeremy Orlow <jorlow@chromium.org>
>> wrote:
>> > On Thu, Nov 11, 2010 at 8:46 PM, Jonas Sicking <jonas@sicking.cc> wrote:
>> >>
>> >> On Thu, Nov 11, 2010 at 5:11 AM, Jeremy Orlow <jorlow@chromium.org>
>> >> wrote:
>> >> > On Mon, Nov 8, 2010 at 2:12 PM, <bugzilla@jessica.w3.org> wrote:
>> >> >>
>> >> >> http://www.w3.org/Bugs/Public/show_bug.cgi?id=11257
>> >> >>
>> >> >>           Summary: Should IDBCursor.update be able to create a new
>> >> >> entry?
>> >> >>           Product: WebAppsWG
>> >> >>           Version: unspecified
>> >> >>          Platform: PC
>> >> >>        OS/Version: All
>> >> >>            Status: NEW
>> >> >>          Severity: normal
>> >> >>          Priority: P2
>> >> >>         Component: Indexed Database API
>> >> >>        AssignedTo: dave.null@w3.org
>> >> >>        ReportedBy: jonas@sicking.cc
>> >> >>         QAContact: member-webapi-cvs@w3.org
>> >> >>                CC: mike@w3.org, public-webapps@w3.org
>> >> >>
>> >> >>
>> >> >> What should happen in the following case:
>> >> >>
>> >> >> db.transaction(["foo"]).objectStore("foo").openCursor().onsuccess =
>> >> >> function(e)
>> >> >> {
>> >> >>  var cursor = e.result;
>> >> >>  if (!cursor)
>> >> >>    return;
>> >> >>
>> >> >>  cursor.delete();
>> >> >>  cursor.update({ id: 1234, value: "Benny" });
>> >> >> }
>> >> >>
>> >> >>
>> >> >> This situation can of course arrive in more subtle ways:
>> >> >>
>> >> >> os = db.transaction(["foo"]).objectStore("foo");
>> >> >> os.openCursor().onsuccess = function(e) {
>> >> >>  var cursor = e.result;
>> >> >>  if (!cursor)
>> >> >>    return;
>> >> >>
>> >> >>  cursor.update({ id: 1234, value: "Benny" });
>> >> >> }
>> >> >> os.delete(1234);
>> >> >>
>> >> >>
>> >> >> As specified, IDBCursor.update behaves just like IDBObjectStore.put
>> >> >> and
>> >> >> just
>> >> >> creates a new entry, but this might be somewhat unexpected behavior.
>> >> >
>> >> > Let's just remove update and delete from IDBCursor and be done with
>> >> > it.
>> >>
>> >> The problem is that you can't always get to the key of the objectStore
>> >> entry to delete/update. Specifically if the objectStore uses
>> >> out-of-line keys the cursor doesn't expose those.
>> >
>> > Why not fix this use case then?  I.e. change the cursor to return
>> > .indexKey,
>> > .primaryKey, .value (or something like that).  If we did this, we could
>> > even
>> > get rid of the different between object cursors and key cursors (which
>> > overload the .value to mean the primary key, which is quite confusing).
>>
>> I would be ok with exposing some new property which exposes the
>> objectstore key.
>
> And thus get rid of the openKeyCursor and getKey?  This would make the spec
> a bit more complicated (we'd need to have 2 IDBCursor objects, one
> that inherits from the other), but seems much simpler to use.  Shall I file
> a bug?

I think openKeyCursor is still needed. There are performance
advantages since you save a btree lookup for each iterated entry, and
you also don't need to spend time reading and possibly deserializing a
potentially large object if all that's needed, for example when doing
a join, is the key.

All I was suggesting is that we have

interface IDBCursor {
  ...
  readonly attribute any objectStoreKey;
  readonly attribute any key;
  readonly attribute any value;
  ...
}

When using a cursor from IDBIndex.openCursor() all three properties
are set. When using a cursor from IDBIndex.openKeyCursor() only
objectStoreKey and key are set. When using a cursor from
IDBObjectStore.openCursor() key and value are set and either we make
objectStoreKey "undefined" or return the same thing as key.

Or, we make IDBObjectStore.openCursor() return a cursor which doesn't
have a objectStoreKey property.

Or we leave things the way they are now.

I'm fine with either of these solutions.

I'm not sure how getKey is affected by all this?

>> But I still think that .update and .delete are useful and logical API
>> which has very little implementation cost.
>
> I still don't understand why you think low implementation is important at
> all when talking about these APIs.  If something is so insanely complex that
> implementors would likely not implement it, then I can understand bringing
> it up, but otherwise I think most people on this list can agree that it
> should cary _very_ little weight when deciding whether API surface area is
> worth it.

For things that are mere convenience APIs I do think that cost of
implementation matters more. Though the type of cost I'm worried about
isn't so much the amount of code that has to be written by
implementations now, but rather how much risk it introduces in terms
of future constraints on the spec and future costs for how
implementations could be written in the future.

In this case there is a direct mapping to other available APIs and so
I think there is very low risk that these functions will come back and
bite us and turn out to have been a bad idea.

It seems to me unlikely that people will only want to do range
operations when reading. Iterating ranges when updating and deleting
seems common too, hence there is a good cost/value ratio.

/ Jonas
Received on Friday, 12 November 2010 06:27:52 GMT

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