[dtp-dev] Suggestion of improvement of catalog loader/sql model extensio

[brian.fitzpatrick@xxxxxxxxxx]

Hi all!

For DTP 1.5 M6, I have a suggestion
of how to make the catalog loader/sql model extension code easier to use
for adopters. I'm interested in getting feedback from the community at
large before delivering this into the codeline.

I've tested this design in the HSQLDB
case (to customize a level - Schema in that case - to use a pipelined tree
content provider and navigator content extension to remove an IVirtualNode
- Stored Procedures) and I've tested it for Derby, which also works to
customize the table loader for Schema nodes and it works great. It greatly
simplifies things by allowing much more reuse and less re-implementing
the wheel to get things done.
 
But I'd like to know what you think.
I'll also be posting this on the newsgroup. 

Thanks for your time!
 
--Fitz
 
Design:

New extension point: org.eclipse.datatools.connectivity.sqm.core.overrideLoader

Each overridden loader element provides four bits of information: product (vendor), version, overriding class (extends one of the JDBCBaseLoader classes), eclass (class name to indicate which model element we are overriding the loader for)

Example:

<extension

        point="org.eclipse.datatools.connectivity.sqm.core.overrideLoader">

        <loader

                provider="org.eclipse.datatools.enablement.hsqldb.catalog.HSQLDBSchemaLoader"

                eclass="org.eclipse.datatools.modelbase.sql.schema.Schema"

                product="HSQLDB"

                version="1.8"/>

</extension>

We would introduce a new manager class to handle these overridden catalog loaders: CatalogLoaderOverrideManager. This class provides three methods:

        getDbDefinitions() returns Iterator of the DbDefinitions with registered overriding catalog loaders

        getEClasses(DatabaseDefinition) returns Iterator of the eclass names with loaders registered for a given database definition

        getLoaderForDatabase ( DatabaseDefinition, eclass name) returns an instance of a class that extends JDBCBaseLoader that can then be cast to a particular type of catalog loader such as JDBCSchemaLoader, JDBCCatalogLoader, etc by the given object

Then each wrapper class in org.eclipse.datatools.connectivity.sqm.core.rte.jdbc (JDBCDatabase, JDBCCatalog, etc.) has code similar to this in its createLoader() method

protected JDBCCatalogLoader createLoader() {

        DatabaseDefinition databaseDefinition = RDBCorePlugin.getDefault().getDatabaseDefinitionRegistry().

                getDefinition(this.getCatalogDatabase());

        JDBCBaseLoader loader =

                CatalogLoaderOverrideManager.getInstance().getLoaderForDatabase(databaseDefinition, SQLSchemaPackage.                                eINSTANCE.getCatalog().getInstanceClassName());

        if (loader != null) {

                JDBCCatalogLoader catLoader = (JDBCCatalogLoader) loader;

                catLoader.setCatalogObject(this);

                return catLoader;

        }

        return new JDBCCatalogLoader(this);

}

If an overriding catalog loader has been registered for a particular db definition/eclass pair, it will be returned here and passed along. If not, we'll stick with the basic method of creating a default catalog loader.

One change was made to JDBCBaseLoader in order to facilitate being created as an executable extension from the plugin extension registry. It had to implement a zero-argument constructor and add a setCatalogObject(ICatalogObject) method.

But this allows anyone implementing custom catalog loaders to use the defaults as much as possible and only start overriding things when they need to.

For example, in the HSQLDB case, we just want to extend the UI wrappers for the model enough to make the Schema object unique for HSQLDB databases. This allows us to then intercept and remove the stored procedure collection node from the UI.

Or in the Derby case, we just want to override the table loader to include Synonyms.


Brian Fitzpatrick
Senior Software Engineer/DTP Committer
Sybase, Inc.