I am currently packaging and distributing the new version of MetaModel - version 1.2. In this blog-post I'll introduce what I think is the most exciting thing introduced in this version: Composite DataContexts aka. "Query multiple datasources with a single query". Or in plain english: You can now treat multiple datastores as if they where one.
An example:
Imagine that you want to match a database table with the contents of an excel spreadsheet, you can easily create a query that reads from both datastores and does all the joining, filtering etc. that is possible with regular MetaModel queries.
DataContext database = DataContextFactory.createJdbcDataContext( myConnection );
DataContext spreadsheet = DataContextFactory.createExcelDataContext(new File("my_spreadsheet.xls");
Table dbTable = database.getDefaultSchema().getTableByName("my_db_table");
Column dbPkColumn = dbTable.getColumnByName("my_primary_key");
Table excelTable = spreadsheet.getDefaultSchema().getTableByName("my_sheet");
Column excelFkColumn = excelTable.getColumnByName("my_foreign_key");
// now we create a composite DataContext which enables us
// to explore and query both DataContexts transparently
// through the same DataContext reference!
DataContext composite = DataContextFactory.createCompositeDataContext( database, spreadsheet );
// example query with carthesian product and cross-datastore where clause
Query q = new Query();
q.from(dbTable).from(excelTable);
q.select(dbTable.getColumns())
q.select(excelTable.getColumns());
q.where(dbPkColumn, OperatorType.EQUALS_TO, excelFkColumn);
DataSet ds = composite.executeQuery(q)
// read the result
... How cool is that?
Of course if a query is posted to the composite DataContext that spans multiple underlaying DataContexts, it will most likely spawn a case of "client side joining" which will not perform well compared to co-locating the datastores. But often that is not possible (or practical if it's just a case of ad-hoc analysis) so I believe that the new composite DataContext feature can add some real value to a lot of projects!
Other notable news in MetaModel 1.2: We now support MS Access databases and dBase (.dbf) database-files.
