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Creating a new step type

This section will summarise the actions involved in creating a new step type and useful APIs you can use. This is mainly described in a checklist fashion.

Creating the step class

Each new step type requires at least the following:

  • Config fields form_define_fields - lists all the fields used as configuration and their properties
  • Validation validate_config - called to validate the configuration stored, and on fail prevents the dataflow from running
  • Execution method execute - the heart of the step. This performs the action of the step.
  • Custom form inputs method form_add_custom_inputs - allows you to define and customise the configuration UI as Moodle form inputs (with tooltips and help text).
  • Unit tests - e.g. demonstrating what it should be able to do.
  • Relevant lang strings added in lang/en/tool_dataflows.php
  • The new class added to lib.php:tool_dataflows_step_types

Wiring together the action in execute()

Several convenience methods have been added to make this process a bit easier. You have:

  • $this->get_config() which returns the configuration of the step, as an object, with all the expressions already evaluated.
  • $this->is_dry_run() which returns whether the dataflow was executed under dry run mode.
  • $this->log() which allows you to log a message during execution which if run directly would print the message to the user.
  • $this->get_variables() which accesses the variables associated with this step.
  • Variables can be exposed when your step gets some new data which you want to make available in other steps. - See variables

For the general gist of how things are structured, please look at the existing examples:

There are some differences between flow, reader and connector steps that may need to be taken into account.

Execute() for flow steps takes in the current value for the iteration (which is also available as the variable 'record'). Your step can modify the value to be passed on to later steps by returning the new value from the execute method.