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Re: [web databases] changeVersion error reporting

From: João Eiras <joaoe@opera.com>
Date: Fri, 04 Sep 2009 04:17:57 +0200
To: "Michael Nordman" <michaeln@google.com>
Cc: "public-webapps@w3.org" <public-webapps@w3.org>
Message-ID: <op.uzpnb7p42q99of@coruscant>

So that was one of the motives to add the creation callback on  
openDatabase I presume.

In either case, before the script gets a Database object, a version check  
needs to be made during openDatabase, so the value can be cached inside  
the Database object, to be used for changeVersion, the version property  
and subsequent transactions.


On Fri, 04 Sep 2009 03:06:37 +0200, Michael Nordman <michaeln@google.com>  
wrote:

> If the version is stored in the database file itself, as is with webkit's
> impl for example, the database object does not have immediate access to  
> that
> value.
> On Thu, Sep 3, 2009 at 5:57 PM, João Eiras <joaoe@opera.com> wrote:
>
>> Hi!
>>
>> Database.changeVersion expects oldVersion and newVersion arguments. The
>> Database also specifies a version attribute.
>> The transaction steps tell to fail the transaction due to the failed
>> preflight condition if oldVersion does not match the current database
>> version.
>> Meanwhile, the callbacks have been made optional, and rightly so.
>>
>> So:
>>  - if the author does not use the callbacks, there no error reporting  
>> that
>> the preflight condition failed
>>  - the version check can be done synchronously when changeVersion is  
>> called
>> because the Database object has immediate access to that value, and it's
>> much more convenient for the author to just get an exception (like
>> INVALID_STATE_ERR) than to have to go through the entire callback  
>> process
>> just to realize later that the transaction failed due to the mismatched
>> version. It also spares the user agent from creating and executing a
>> transaction that WILL fail.
>>
>> To solve these issues, I would suggest doing immediate synchronous
>> validation of the version when changeVersion is called, throwing an
>> exception on error, and drop that step from the preflight operations.
>>
>> Thank you.
>>
Received on Friday, 4 September 2009 02:18:44 GMT

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