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Pentaho Documentation

Store the Processing State

The class implementing StepInterface does not store processing state in any of its fields. Instead an additional class implementing StepDataInterface is used to store processing state, including status flags, indexes, cache tables, database connections, file handles, and alike. Implementations of StepDataInterface declare the fields used during row processing and add accessor functions.  In essence the class implementing StepDataInterface is used as a place for field variables during row processing.

PDI creates instances of the class implementing StepDataInterface at the appropriate time and passes it on to the StepInterface object in the appropriate method calls. The base class already implements all necessary interactions with PDI and there is no need to override any base class methods.