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RE: [indexeddb] openCursor optional parameters issue

From: Eliot Graff <Eliot.Graff@microsoft.com>
Date: Fri, 8 Jul 2011 00:24:23 +0000
To: Jonas Sicking <jonas@sicking.cc>, Israel Hilerio <israelh@microsoft.com>
CC: "public-webapps@w3.org" <public-webapps@w3.org>, Adam Herchenroether <aherchen@microsoft.com>, Victor Ngo <vicngo@microsoft.com>
Message-ID: <CE3A5BFD1228D84A8D9C158EEC195FD53CC9A5C6@TK5EX14MBXW601.wingroup.windeploy.ntdev.microsoft.com>
Done and pushed to Mercurial.

Updated sync and async versions of openCursor on ObjectStore and Index as follows:
made type of 'range' equal to any
made 'range' nullable

Eliot

> -----Original Message-----
> From: public-webapps-request@w3.org [mailto:public-webapps-
> request@w3.org] On Behalf Of Jonas Sicking
> Sent: Thursday, June 30, 2011 2:30 PM
> To: Israel Hilerio
> Cc: public-webapps@w3.org; Adam Herchenroether; Victor Ngo
> Subject: Re: [indexeddb] openCursor optional parameters issue
> 
> On Thu, Jun 30, 2011 at 1:19 PM, Israel Hilerio <israelh@microsoft.com>
> wrote:
> > On Tuesday, June 28, 2011 7:31 PM, Jonas Sicking wrote:
> >> On Tue, Jun 28, 2011 at 4:59 PM, Israel Hilerio
> >> <israelh@microsoft.com>
> >> wrote:
> >> > On Tuesday, June 28, 2011 12:49 PM, Jonas Sicking wrote:
> >> >> On Tue, Jun 28, 2011 at 10:53 AM, Israel Hilerio
> >> >> <israelh@microsoft.com>
> >> >> wrote:
> >> >> > On Monday, June 27, 2011 8:21 PM, Jonas Sicking wrote:
> >> >> >> On Mon, Jun 27, 2011 at 11:42 AM, Israel Hilerio
> >> >> >> <israelh@microsoft.com>
> >> >> >> wrote:
> >> >> >> > The IDBObjectStore.openCursor method is defined to have two
> >> >> >> > optional
> >> >> >> parameters:
> >> >> >> > * IDBRequest openCursor (in optional any range, in optional
> >> >> >> > unsigned short direction) raises (IDBDatabaseException);
> >> >> >> >
> >> >> >> > Based on the examples in the spec, it seems we're envisioning
> >> >> >> > the method
> >> >> >> to be used in the following ways:
> >> >> >> > * objStore.openCursor();
> >> >> >> > * objStore.openCursor(keyRange);
> >> >> >> > * objStore.openCursor(keyRange, IDBCursor.PREV);
> >> >> >> > * objStore.openCursor(IDBCursor.PREV);
> >> >> >>
> >> >> >> No, that's not how optional parameters work in WebIDL. In order
> >> >> >> to specify an optional parameter, you always have to specify
> >> >> >> all preceding optional parameters. So only the following
> >> >> >> syntaxes are
> >> >> >> valid:
> >> >> >>
> >> >> >> * objStore.openCursor();
> >> >> >> * objStore.openCursor(keyRange);
> >> >> >> * objStore.openCursor(keyRange, IDBCursor.PREV);
> >> >> >>
> >> >> >> > Having "any" for the keyRange type makes it difficult to
> >> >> >> > detect the correct
> >> >> >> overloaded parameter for openCursor.
> >> >> >>
> >> >> >> The reason the first parameter is of type 'any' is so that you
> >> >> >> can pass either a IDBKeyRange or a value. So for example:
> >> >> >>
> >> >> >> req = objStore.openCursor("hello"); req = index.openCursor(4);
> >> >> >>
> >> >> >> are valid. When called with a simple value on an object store
> >> >> >> the cursor will obviously always return 0 or 1 rows. For
> >> >> >> indexes it could return any number of rows though.
> >> >> >>
> >> >> >> This is actually already specified if you look at the steps for
> >> >> >> opening a
> >> >> cursor.
> >> >> >> The same holds true for many other functions, such as .get and
> .delete.
> >> >> >>
> >> >> >> However it's a very subtle feature that's easy to miss. If you
> >> >> >> have suggestions for how to make this more clear in the spec
> >> >> >> I'd love to hear them. I've been thinking that we should add
> >> >> >> non-normative, easy-to-understand text to explain each
> >> >> >> function, similar to what the
> >> >> >> HTML5 spec does when defining APIs.
> >> >> >>
> >> >> >> / Jonas
> >> >> >
> >> >> > What you're saying makes a lot of sense.  That was what I
> >> >> > originally thought
> >> >> but what confused me was some of the examples in the current spec
> >> >> which suggest we want to do the following (Section 3.3.5):
> >> >> > * objStore.openCursor(IDBCursor.PREV);
> >> >>
> >> >> I don't think we should allow this. The benefit of saving the
> >> >> author from writing objStore.openCursor(nulll, IDBCursor.PREV)
> >> >> isn't worth the complexity that is introduced. IMHO. We should
> >> >> just fix the example
> >> instead.
> >> >>
> >> >> > Independent of how up to date the examples are, the issue with
> >> >> > the way it is
> >> >> currently spec'ed is that there is an implied dependency between
> >> >> keyRange and Cursor direction.  In other words, you can't open a
> >> >> cursor without any keyRange and just a direction.  One possible
> >> >> way to resolve this is to allow the keyRange to be nullable.  This
> >> >> will allow us to define a cursor without a keyRange and with a direction:
> >> >> > * objStore.openCursor(null, IDBCursor.PREV);
> >> >> >
> >> >> > Without something like this, it is not easy to get a list of all
> >> >> > the records on
> >> >> the store going in the opposite direction from IDBCursor.NEXT.
> >> >>
> >> >> Indeed, it was the intent that this should be allowed. I suspect
> >> >> we simply haven't kept up to date with WebIDL changing under us.
> >> >> But I do think that the text in the algorithm does say to do the
> >> >> right thing when no keyrange (or key
> >> >> value) is supplied.
> >> >>
> >> >> / Jonas
> >> >
> >> > My concern is not having a clean mechanism to retrieve a regular
> >> > cursor
> >> with an inverted order without knowing any records (first or last) in
> >> the list.  This seems like a common operation that is not supported today.
> >> >
> >> > These are some of the alternatives that I believe we have:
> >> > * Support a null value for IDBKeyRange:
> >> >        -IDBRequest objStore.openCursor(null, IDBCursor.PREV);
> >> > * Introduce a new specialized method to handle this scenario:
> >> >        -IDBRequest objStore.openDirectionalCursor(IDBCursor.PREV);
> >> >         * This will default internally to an IDBKeyRange with the
> >> > properties
> >> defined below.
> >> >         * One advantage of this approach is that we don't have to
> >> > expose a new
> >> IDBKeyRange constructor.
> >> > * Define a new static keyRange constructor that is a catch all:
> >> >        -static IDBKeyRange.all();
> >> >         * The values for the new constructor would be:
> >> >                IDBKeyRange.lower = undefined
> >> >                IDBKeyRange.upper = undefined
> >> >                IDBKeyRange.lowerOpen = false
> >> >                IDBKeyRange.upperOpen = false
> >> >         * I believe these satisfy the conditions for a key is in a
> >> > key range section
> >> [1].
> >> >
> >> >         * We could pass this new keyRange to the existing openCursor
> method:
> >> >            -objStore.openCursor(IDBKeyRange.all(), IDBCursor.PREV);
> >> >
> >> > Let me know if you see any other alternatives or if you like any of
> >> > these
> >> options.
> >> >
> >> > Israel
> >> > [1]
> >> > http://dvcs.w3.org/hg/IndexedDB/raw-file/tip/Overview.html#dfn-in-a
> >> > -ke
> >> > y-range
> >>
> >> I think we're talking past each other. I was trying to say that when
> >> I wrote the current spec text, my intent was for
> >>
> >> req = objStore.openCursor(null, IDBCursor.PREV);
> >>
> >> to work and return a cursor which iterates the whole object store.
> >> Same for indexes of course. The "Cursor Iteration Operation" should
> >> already support this unless I've made a mistake somewhere.
> >>
> >> What's happened is that since I wrote the text WebIDL changed in such
> >> a way that it now requires types to be explicitly nullable. However I
> >> don't think that applies to the 'any' type used for most cursor-open
> functions.
> >>
> >> However I do now see that the type defined for the open-cursor
> >> functions on indexes use "IDBKeyRange" rather than "any" as type.
> >> That needs to be fixed (In both sync and async) such that you can do
> >> things like
> >>
> >> req = myindex.openCursor(4);
> >> and
> >> req = myindex.openKeyCursor("hello", IDBCursor.PREV);
> >>
> >> / Jonas
> >
> > Great, thanks for clarifying!  Yes, I believe we are in violent
> > agreement :-)
> >
> > To avoid future confusion, I believe we should update the WebIDL table
> associated with IDBObjectStore.openCursor and IDBIndex.openCursor to add
> a checkmark in the Nullable field instead of an x.  Plus as you pointed out, we
> need to ensure the type arguments are the same for both of these two
> methods (add the any and replace the IDBKeyRange).
> >
> > I can work with Eliot on this.
> 
> Sounds great! Thanks!
> 
> / Jonas
> 
Received on Friday, 8 July 2011 00:25:06 GMT

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