Re: [Hsqldb-developers] Updatable resultsets

[fredt <fr...@us...>]

I exchanged a couple of emails with Moray who expressed an interest in
studying the code with a view to help implement this feature. Here is what I
thought needs doing. As these steps are in different areas of code, anyone
who wants to help is welcome.

The steps are [with a few refinements]:

- Support SELECT ... FOR UPDATE. This means checks are performed on the
query _after_ compilation to ensure it does not contains constructs that are
not allowed (e.g. sum(*)). The method to do this will be similar to
org.hsqldb.Select.resolvAll() and the methods that are called from it. The
check
will simply throw if certain types of org.hsqldb.Expression are encountered

- The Select object will have extra columns tagged to the end with primary
key columns of all the tables involved. The columns are in
org.hsqldb.Select.eColumn

- A new type of org.hsqldb.Result is added, which is similar to
ResultConstants.DATA.
This will be used to read back the updated ResultSet.

- Method definitions for org.hsqldb.jdbcResultSet.setXXX are added, similar
to
jdbcPreparedStatement.setXXX

- A new method is added somewhere to use this result set to update the
affected rows directly. This method will be similar to
org.hsqldb.CompiledStatementExecutor.executeUpdateStatement()

- Some additional flags and state variables will have to be added here and
there to take care of transactions and cases where rows have changed between
the creation of the ResultSet and the updates.

- Maybe a bit more work on transactions than I mentioned above

Fred

----- Original Message -----
From: "Moray Taylor" <mt...@lo...>
To: <hsq...@li...>
Sent: 13 October 2003 10:13
Subject: [Hsqldb-developers] Updatable resultsets


Hi,

Short Version: Are there any plans to implement updatable resultsets,
i.e. insertRow(), updateObject()?

Long Version: I am writing an application that is basicaly a database
client, at the moment, it works with MySQL, PostGres, and DB2. I'd
really like to add the option for an embedded DB, HSQLDB seems perfect
for this, apart from one thing, I need updatable ResultSets. For
insertRow(), I could work around it by doing it 'old school' with
INSERTs, but it wouldn't be as nice. For updateObject()/updateString()
etc.., I don't see a workaround.

I am happy to contribute code, beta-testing etc... but I don't have
much experience with writing JDBC interfaces, just using them, so I'm
not sure if I'd be much use.

Thanks

Moray



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