On Thu, Apr 28, 2011 at 10:44 AM, Andrea Aime
<[email protected]>wrote:
> On Thu, Apr 28, 2011 at 6:35 PM, Justin Deoliveira <[email protected]>
> wrote:
> > Hi all,
> > I wanted to get some feedback on a problem i am trying to solve and a
> > possible solution. First the problem.
> > It comes out of working on the teradata datastore. The td database has a
> > feature called "query banding". It is very simple in nature. It is
> basically
> > just a statement that sets some key value pairs before another statement
> is
> > executed, or set some key value pairs for the life of a connection. A
> common
> > example is to set the name of the application. So one might do:
> > SET QUERY_BAND = 'Application = geotools`;
> > SELECT * FROM ...;
> > I am not that familiar with how it is used but it generally gets used for
> BI
> > type applications, and for workload management. So that the database can
> for
> > instance prioritize queries for a particular application. The client
> funding
> > the td datastore ask that the query banding feature be utilized.
> > Anyways, that said the problem is basically that I need to be able to set
> > certain query bands before statements executed by the jdbc datastore.
> > And currently don't have a great mechanism to do so since it is really
> out
> > of the dialect hands.
> > The best solution I can come up with is to add some callback methods to
> the
> > dialect that the datastore will call before it executes a statement. For
> > example:
> > BasicSQLDialect {
> > onSelect(Statement st, Connection cx, FeatureType);
> > onDelete(Statement st, Connection cx, FeatureType);
> > onInsert(Statement st, Connection cx, FeatureType);
> > onUpdate(Statement st, Connection cx, FeatureType);
> > }
> > PreparedSQLDialect {
> > onSelect(PreparedStatement st, Connection cx, FeatureType);
> > onDelete(PreparedStatement st, Connection cx, FeatureType);
> > onInsert(PreparedStatement st, Connection cx, FeatureType);
> > onUpdate(PreparedStatement st, Connection cx, FeatureType);
> > }
>
> I am wondering if we could extend the following method instead:
>
> /**
> * Initializes a newly created database connection.
> * <p>
> * Subclasses should override this method if there is some
> additional action
> * that needs to be taken when a new connection to the database is
> created. The
> * default implementation does nothing.
> * </p>
> * @param cx The new database connection.
> */
> public void initializeConnection( Connection cx ) throws SQLException {
>
> }
>
>
> Another question is, how do you plan to send down the kvp to be
> set in the connection?
> Right now the store understands view params, but conceivably one might
> want to use query banding and view params at the same time.
>
Well the query bands being requested are pretty specific, and not arbitrary
or supplied on the fly. The client has requested the following:
Application - By default "GeoTools", but overridden to "GeoServer" or "uDig"
when run from those applications
ClientUser - The authenticated user (in geoserver) if applicable.
ClientHostName - Same as above
Layer - The layer name being (possibly the geoserver layer name) being
queried, etc...
The Application qb is session local and the rest are statement local. The
former will be specified as a datastore connection param. The latter I was
thinking I would make use of EnvFunction to set some thread local values.
And then add a filter to the geoserver teradata function to set them.
>
> Cheers
> Andrea
>
>
> --
> -------------------------------------------------------
> Ing. Andrea Aime
> GeoSolutions S.A.S.
> Tech lead
>
> Via Poggio alle Viti 1187
> 55054 Massarosa (LU)
> Italy
>
> phone: +39 0584 962313
> fax: +39 0584 962313
>
> http://www.geo-solutions.it
> http://geo-solutions.blogspot.com/
> http://www.youtube.com/user/GeoSolutionsIT
> http://www.linkedin.com/in/andreaaime
> http://twitter.com/geowolf
>
> -------------------------------------------------------
>
--
Justin Deoliveira
OpenGeo - http://opengeo.org
Enterprise support for open source geospatial.
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