Creating a Blank Flow without a Trigger

A Flogo App, can contain a flow that is independent of one or more triggers that will eventually activate the flow. This method of creating a flow is useful when you have the logic for the flow but do not know yet what action should cause the flow to activate. You can start by creating a flow first and attach one or more triggers to the flow at a later time. A blank flow is akin to a function that has input parameters and return parameters.

Note: When executing a flow with multiple triggers, you cannot disable a trigger, specify a particular trigger to execute, or specify the order in which the triggers execute. All triggers get initialized in the order that they were specified in the flow.

The output of a trigger provides the input to the flow. Hence, it must be mapped to the flow input. In the absence of a trigger, when creating a flow, there must be a well defined contract within the flow which specifies the input to the flow and the output expected after the flow completes execution. You define this contract in the Flow Inputs & Outputs dialog. The Flow Inputs & Ouputs contract works as a bridge between the flow and the trigger, hence every trigger has to be configured to map its output to the Input parameters defined in Flow Inputs & Ouputs.

If any trigger needs to send a response back to a server, its output must be mapped to the output of the Return activity.

Follow these steps to create a blank flow:

Procedure

  1. If you selected Create a blank flow in the Create a flow dialog, the flow gets created and you will be prompted to either start from a trigger or configure your flow contract. Select Configure Flow Inputs & Outputs. The page opens displaying the Inputs and the Outputs tabs.

  2. Enter a JSON schema containing the input fields to the flow in the Inputs tab and the JSON schema containing the flow output fields in the Outputs tab. Click the left facing arrow on top of the blue label when done to retract the Flow Inputs & Outputs page.
  3. On creation, a blank flow contains a Return activity by default. Click and drag the Return activity to the right to make room to add other activities.
  4. Hover your mouse over the shaded square to expose the add activity button (). Click the add activity button to add an activity.
    After adding an activity, be sure to configure its properties by clicking on the activity tile. If one or more activities are not configured properly in a flow, the Errors panel on the lower right of the page shows the number of errors in the flow. Click the Errors panel to see the errors.

    Fix the errors before proceeding.

  5. Continue adding activities by clicking the successive () buttons. To add an activity in between two exisiting activities, you can drag the activities to the right in order to make room for the new activity then click the button to add the new activity.
  6. Click the Return activity to configure the parameters that the flow outputs after completing execution. The Input tab of the Return activity displays the parameters that you had configured in the Output tab of the Flow Inputs & Outputs dialog. Be sure to map the Return activity Input parameters to parameters that you want the flow to return.

    Anything that the flow outputs after execution must be mapped into the Return activity of the flow. If any trigger needs to send a response back to a server, its output must be mapped to the output of the Return activity.

  7. When you are ready to add a trigger, refer to Adding Triggers to a Flow to add one or more triggers to the flow. Be sure to map the trigger output to the flow input that you have defined in the Input tab of the Flows Inputs & Outputs dialog. For triggers that need to send back a response following the execution of the flow, you must map the flow output to the reply of the trigger.
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