Working with the Relations Data Unit

Please prepare teh DPU 'MyDpu' as described in Working with the Relations Data Unit.

To read tables from the input data unit, one has to define the input Relational data unit.

Code 1 - defining input data unit

 @DataUnit.AsInput(name = "input")
 public RelationalDataUnit input;

All data units must be public with proper annotation: they must at least contain a name, which will be the name visible in the UnifiedViews administration interface for pipeline developers. The code above goes to the main DPU class.

In order to work with input data unit, you typically use RelationalHelper class (eu.unifiedviews.helpers.dataunit.relational.RelationalHelper in uv-dataunit-helpers ).

RelationalHelper class provides methods to get a list of tables, the input Relational data unit contains to operate with them:

Code 2 shows how the method for getting tables can be used (The code below goes to innerExecute() method of the DPU).

Code 2 - Iterating over input RDF graphs using RDFHelper

try {
        Set<RelationalDataUnit.Entry> tableEntries = RelationalHelper.getTables(input);
} catch (DataUnitException ex) {
   throw ContextUtils.dpuException(ctx, ex, "dpuName.error");
}

By having the set of tables, you may then iterate over tableEntries as follows:

Code 3 - Getting dataset

try {
    Set<RelationalDataUnit.Entry> tables = RelationalHelper.getTables(inputTables);
    for (RelationalDataUnit.Entry table : tables) {
            String tableName = table.getTableName();
    }
} catch (DataUnitException e) {
    throw ContextUtils.dpuException(ctx, e, "dpuName.error");
}

By getting data from the input tables, the best is to obtain an SQL Connection to the input data unit input:

Code 4 - Getting connection

Connection databaseConnection = input.getDatabaseConnection();

Please prepare DPU 'MyDpu' as described in Working with the Relations Data Unit. To write tables to the output data unit, one has to define the output Relational data unit.

Code 4 - defining output data unit

@DataUnit.AsOutput(name = "output")
public WritableRelationalDataUnit output;

All data units must be public with proper annotation: they must at least contain a name, which will be the name visible in the UnifiedViews administration interface for pipeline developers. The code above goes to the Main DPU class.

In order to work with output data unit, you use directly the methods from the data unit WritableRelationalDataUnit API:

Code 5 - new table

output.addNewDatabaseTable("myOutputTable"); 

There are default settings. If those are not enough, you may customize them in the config.properties file:

By default UnifiedViews uses H2 database in embedded mode, using files to store the tables.

Database file name (file DB mode):

dbFileName.append("dataUnitDb");

dbFileName.append("_");

dbFileName.append(this.executionId);

TODO: RelationalHelper class (eu.unifiedviews.helpers.dataunit.rdf.RelationalHelper in uv-dataunit-helpers ) for writing tables.