HTML 5 Web SQL Database Transaction commit or rollback when refreshing page

Question

As written in the Safari Client-Side Storage and Offline Applications Programming Guide, rolling back a HTML 5 Web SQL Database transaction is done by returning true in the callback function provided as an error callback to a transaction the executeSql method:

The per-query error-handling callback is rather straightforward. If the callback returns true, the entire transaction is rolled back. If the callback returns false, the transaction continues as if nothing had gone wrong. Thus, if you are executing a query that is optional—if a failure of that particular query should not cause the transaction to fail—you should pass in a callback that returns false. If a failure of the query should cause the entire transaction to fail, you should pass in a callback that returns true.

For example if I have the following transaction (suppose the 'users' table has a UNIQUE constraint on the 'username' field and username 'test' already exists - which I'm trying to insert again, which should result in a constraint error):

database.transaction(function(transaction) {
    transaction.executeSql(
        "INSERT INTO users (username) VALUES('test')",
        null,
        dataCallback,
        errorCallback
     );
});

function errorCallback() {
    return true; //this causes the rollback
}

I have two questions:

1. If I have to include many operations inside a transaction (for example I have to send some data using ajax to a server and wait for the response, etc.) and the user reloads the page before the response had arrived (which means that the errorCallback won't be called), will the transaction be commited or will it fail ?

2. Does anyone know how to rollback a Web SQL transaction manually ? For example if I want to rollback a transaction based on the result of an ajax call, how can it be done ? Should I run a query which contains an error to make sure that the error callback is called ?

Thanks.

Answer 1

1. The transaction will be committed.
2. Yes, to rollback explicitly, you must invoke invalid query explicitly. This is recommended workaround since the quick-and-dirty API is missing abort method.

Regarding AJAX, be ready all data, before you start a write transaction. You won't have any problem as you described. Use database constraint (UNIQUE, FOREIGNKEY) as much possible.