On Jul 27, 2009, at 12:55 PM, Nikunj R. Mehta wrote:
On Jul 25, 2009, at 1:18 PM, Aaron Boodman wrote:
But using workers is a large burden: they are
completely separate JavaScript environments that share nothing with
the main web page. Having to use that for simpler use cases would be
very unfortunate.
I am not sure how large a burden this is. Can you quantify it? Can
you explain why this would be unacceptable?
The cost of using a Worker is that all interaction with the actual Web
page and its data is through an asynchronous channel that only allows
transfer of relatively simple pure data objects (essentially, JSON).
The advantage is that you can write database access as simple straight-
line code. If you want to do a lot of database work and don't need to
interact with page contents or associated JavaScript data structures
in the middle or very extensively, a Worker using the synchronous API
will likely work well. If you only want to do a little bit of database
access, or you need to mix it heavily with page interaction, using the
async API from the main thread will likely be simpler.
The programming model espoused by WebDatabase's async portion is that:
1. the programmer does all the SQL work in one or more asynchronous
callbacks.
2. callbacks are always linear, however, the program performs its
own stack management to keep the requisite context around for doing
its processing inside asynchronous callbacks. If multiple calls to
the database are required to perform certain work, then the programs
become a chain of nested callbacks.
3. the only supported model of transaction isolation is
serialization of all database access.
This is certainly foreign to most database developers. Editors and/
or others share the burden of proof that there is no alternative to
this and that there is merit in standardizing a brand new
programming model.
JavaScript actually lets you write a series of nested callbacks in a
way that looks almost like straight-line code, by using function
expressions:
db.transaction(function(tx) {
tx.executeSQL("SELECT UserID FROM Users WHERE UserName = ?",
[userToBan], function(tx, firstResultSet) {
if (resultSet.rows.length > 0) {
tx.executeSQL("INSERT INTO BannedUsers VALUES (?)",
resultSet.rows[0]);
}
}
});
(Sorry for the contrived example and my likely syntax errors.)
Granted, this gets awkward if your logic gets considerably more
complicated.
Regards,
Maciej
