Re: [IndexedDB] Events and requests

On Tue, Nov 9, 2010 at 11:35 AM, Jonas Sicking <jonas@sicking.cc> wrote:

> Hi All,
>
> One of the things we briefly discussed at the summit was that we
> should make IDBErrorEvents have a .transaction. This since we are
> allowing you to place new requests from within error handlers, but we
> currently provide no way to get from an error handler to any useful
> objects. Instead developers will have to use closures to get to the
> transaction or other object stores.
>
> Another thing that is somewhat strange is that we only make the result
> available through the success event. There is no way after that to get
> it from the request. So instead we use special event interfaces with
> supply access to source, transaction and result.
>
> Compare this to how XMLHttpRequests work. Here the result and error
> code is available on the request object itself. The 'load' event,
> which is equivalent to our 'success' event didn't supply any
> information until we recently added progress event support. But still
> it only supplies information about the progress, not the actual value
> itself.
>
> One thing we could do is to move
>
> .source
> .transaction
> .result
> .error
>
> to IDBRequest. Then make "success" and "error" events be simple events
> which only implement the Event interface. I.e. we could get rid of the
> IDBEvent, IDBSuccessEvent, IDBTransactionEvent and IDBErrorEvent
> interfaces.
>
> We'd still have to keep IDBVersionChangeEvent, but it can inherit
> Event directly.
>
> The request created from IDBFactory.open would return a IDBRequest
> where .transaction and .source is null. We already fire a IDBEvent
> where .source is null (actually, the spec currently doesn't define
> what the source should be I see now).
>
>
> The only major downside with this setup that I can see is that the
> current syntax:
>
> db.transaction(["foo"]).objectStore("foo").get(mykey).onsuccess =
> function(e) {
>  alert(e.result);
> }
>
> would turn into the slightly more verbose
>
> db.transaction(["foo"]).objectStore("foo").get(mykey).onsuccess =
> function(e) {
>  alert(e.target.result);
> }
>
> (And note that with the error handling that we have discussed, the
> above code snippets are actually plausible (apart from the alert() of
> course)).
>
> The upside that I can see is that we behave more like XMLHttpRequest.
> It seems that people currently follow a coding pattern where they
> place a request and at some later point hand the request to another
> piece of code. At that point the code can either get the result from
> the .result property, or install a onload handler and wait for the
> result if it isn't yet available.
>
> However I only have anecdotal evidence that this is a common coding
> pattern, so not much to go on.
>

Here's a counter proposal:  Let's add .transaction, .source, and .result to
IDBEvent and just specify them to be null when there is no transaction,
source, and/or result.  We then remove readyState from IDBResult as it
serves no purpose.

What I'm proposing would result in an API that's much more similar to what
we have at the moment, but would be a bit different than XHR.  It is
definitely good to have similar patterns for developers to follow, but I
feel as thought the model of IndexedDB is already pretty different from XHR.
 For example, method calls are supplied parameters and return an IDBRequest
object vs you using new to create the XHR object and then making method
calls to set it up and then making a method call to start it.  In fact, if
you think about it, there's really not that much XHR and IndexedDB have in
common except that they use event handlers.

As for your proposal, let me think about it for a bit and forward it on to
some people I know who are playing with IndexedDB already.

J