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Re: [IndexedDB] Passing an empty array to IDBDatabase.transaction

From: Joshua Bell <jsbell@chromium.org>
Date: Mon, 17 Oct 2011 15:15:02 -0700
Message-ID: <CAD649j5jSs1FYrb0+zS_++JP2d_-UeVGn5ADKTwZkACC4pVMew@mail.gmail.com>
To: "public-webapps@w3.org" <public-webapps@w3.org>
On Fri, Oct 14, 2011 at 4:02 PM, Israel Hilerio <israelh@microsoft.com>wrote:

> On Friday, October 14, 2011 3:57 PM, Jonas Sicking wrote:
> > On Fri, Oct 14, 2011 at 2:57 PM, Israel Hilerio <israelh@microsoft.com>
> > wrote:
> > > On Friday, October 14, 2011 2:43 PM, Jonas Sicking wrote:
> > >> On Fri, Oct 14, 2011 at 2:27 PM, Israel Hilerio
> > >> <israelh@microsoft.com>
> > >> wrote:
> > >> > On Monday, October 10, 2011 10:15 AM, Israel Hilerio wrote:
> > >> >> On Monday, October 10, 2011 9:46 AM, Jonas Sicking wrote:
> > >> >> > On Fri, Oct 7, 2011 at 11:51 AM, Israel Hilerio
> > >> >> > <israelh@microsoft.com>
> > >> >> > wrote:
> > >> >> > > On Thursday, October 06, 2011 5:44 PM, Jonas Sicking wrote:
> > >> >> > >> Hi All,
> > >> >> > >>
> > >> >> > >> In both the Firefox and the Chrome implementation you can
> > >> >> > >> pass an empty array to IDBDatabase.transaction in order to
> > >> >> > >> create a transaction which has a scope that covers all
> > >> >> > >> objectStores in the database. I.e. you can do something like:
> > >> >> > >>
> > >> >> > >> trans = db.transaction([]);
> > >> >> > >> trans.objectStore(<any objectstore here>);
> > >> >> > >>
> > >> >> > >> (Note that this is *not* a dynamic scoped transaction, it's
> > >> >> > >> still a static scope that covers the whole database).
> > >> >> > >>
> > >> >> > >> In other words, these implementations treat the following two
> > >> >> > >> lines as
> > >> >> > >> equivalent:
> > >> >> > >>
> > >> >> > >> trans = db.transaction([]);
> > >> >> > >> trans = db.transaction(db.objectStoreNames);
> > >> >> > >>
> > >> >> > >> This, however, is not specified behavior. According to the
> > >> >> > >> spec as it is now the transaction should be created with an
> empty
> > scope.
> > >> >> > >>
> > >> >> > >> I suspect both Mozilla and Google implemented it this way
> > >> >> > >> because we had discussions about this syntax on the list.
> > >> >> > >> However apparently this syntax never made it into the spec. I
> > >> >> > >> don't
> > >> recall why.
> > >> >> > >>
> > >> >> > >> I'm personally not a big fan of this syntax. My concern is
> > >> >> > >> that it makes it easier to create a widely scoped transaction
> > >> >> > >> which has less ability to run in parallel with other
> > >> >> > >> transactions, than to create a transaction with as narrow
> scope as
> > possible.
> > >> >> > >> And passing
> > >> >> > db.objectStoreNames is always possible.
> > >> >> > >>
> > >> >> > >> What do people think we should do? Should we add this
> > >> >> > >> behavior to the spec? Or are implementations willing to remove
> it?
> > >> >> > >>
> > >> >> > >> / Jonas
> > >> >> > >>
> > >> >> > >
> > >> >> > > Our implementation interprets the empty array as an empty
> scope.
> > >> >> > > We
> > >> >> > allow the transaction to be created but we throw a NOT_FOUND_ERR
> > >> >> > when trying to access any object stores.
> > >> >> > > I vote for not having this behavior :-).
> > >> >> >
> > >> >> > Hi Israel,
> > >> >> >
> > >> >> > I just realized that I might have misinterpreted your response.
> > >> >> >
> > >> >> > Are you saying that you think that passing an empty-array should
> > >> >> > produce a transaction with an empty scope (like in IEs
> > >> >> > implementation and as described by the spec currently), or a
> > >> >> > transaction with every objectStore in scope (like in Firefox and
> > chrome)?
> > >> >> >
> > >> >> > / Jonas
> > >> >> >
> > >> >>
> > >> >> We don't do it like FF or chrome.  We create the transaction but
> > >> >> it has an empty scope transaction.  Therefore, whenever you try to
> > >> >> access an object store we throw an exception.  Based on what Hans
> > >> >> said, it seems we're all in agreement.
> > >> >>
> > >> >> Also, I like Ben's suggestion of not allowing these transactions
> > >> >> to be created in the first place and throwing an exception during
> > >> >> their
> > >> creation.
> > >> >>
> > >> >> Israel
> > >> >>
> > >> >
> > >> > What type of exception should we throw when trying to create a
> > >> > transaction
> > >> with an empty scope (NotFoundError, TypeError, or other)?
> > >>
> > >> Either of those would work for me.
> > >>
> > >> / Jonas
> > >
> > > We would like to go with NotFoundError.  The reason is that an empty
> array
> > is still the correct type and therefore a TypeError would seem strange.
> >
> > Just noticed "InvalidAccessError" which seems like it could be a good fit
> too.
> >
> > / Jonas
> >
>
> I like that better!  Seems to match closer the reason for the failure.
>
> Israel
>
>
While this is top-of-mind, is there any desire to eliminate the case of
special passing a string into IDBDatabase.transaction() for the storeNames
parameter, versus a DOMStringList/Array? That case is documented in the
spec, is currently functional in Chrome and has partial test coverage. It
doesn't have the same potentially hidden performance concerns that the []
shortcut does, but it is a special case and requires pushing interpretation
and validation of the parameter's type from IDL binding into IDB-specific
code.
Received on Monday, 17 October 2011 22:15:29 GMT

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