The MetaModel project lets you do wonderful and advanced things like filtering, ordering, grouping etc. when working with otherwise static content in CSV files, Excel spreadsheets, XML files etc. Many times I have knocked my head to the door when trying to get simple summary data out of my excel spreadsheets or simply filtering on single rows in the sheets.
An example: Recently I was working on my tax return statement and throughout the year I had recorded all relevant activities in a simple spreadsheet. I had marked the activities on various accounts such as representation, spendings, earnings whatever. Simplified it looked something like this:
| Title | Amount | Account |
|---|---|---|
| Asus EEE | 1.600 | Spendings |
| Advisory for Company X | 4.000 | Earnings |
One thing I think is funny when dealing with Excel is that throughout time you've learned how to set up your spreadsheet for easy hacking instead of dynamic querying. What I mean by this is that if I wanted to get SUM for each account in my spreadsheet I would propbably have fundamentally changed my (otherwise nice and pure) spreadsheet in order to make it easy to perform the SUM function on singular accounts. For example I may have introduced an ammount column for each account. But alas, adding a new Account would be pretty cumbersome.
Enter MetaModel! With MetaModel I can write queries in a SQL-like manner. When I say "SQL-like" you may fret and think "oh but don't learn me another SQL dialect, just give me the real deal!". The answer to this is that what I'll learn you now will effectively replace all SQL dialects because the same model (or MetaModel ;)) is usable for all kinds of datastores: Excel, CSV/TSV files, XML and SQL-databases). Let's have a look at some code. First we'll load the Excel file into MetaModel and get a hold of our schema and table structure and identify our columns of interest:
// Use the factory to create a DataContext and automatically (true) narrow column types
DataContext dataContext = DataContextFactory.createExcelDataContext(new File("my_tax_return_activities.xls"), true);
Schema schema = dataContext.getDefaultSchema();
// A simple way of getting the table object is just to pick the first one (the first sheet in the spreadsheet)
Table table = schema.getTables()[0];
Column amountColumn = table.getColumnByName("Amount");
Column accountColumn = table.getColumnByName("Account");
Now that we have the columns represented and the DataContext which we can use to perform queries, here's how we make a couple of interesting queries using the MetaModel query API:
// SELECT SUM(Amount) FROM sheet WHERE Account = "Spendings"
Query q = new Query().select(new SelectItem(FunctionType.SUM, amountColumn)).from(table).where(accountColumn, OperatorType.EQUALS_TO, "Spendings");
// SELECT Account, SUM(Amount) FROM sheet GROUP BY Account
Query q = new Query().select(accountColumn).select(new SelectItem(FunctionType.SUM, amountColumn)).from(table).groupBy(accountColumn);
Now when we've authored the queries we can let MetaModel execute them and deal with the result as appropriate. If we just want to print out the results to the console we'll do something like this:
DataSet dataSet = dataContext.executeQuery(q);
while (dataSet.next()) {
System.out.println(dataSet.getRow());
}
dataSet.close();
