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transformations:repeat

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REPEAT

Category: Workflow / Internal


Description

The Repeat action allows for arranging "DO…WHILE" and "DO…UNTIL" types of loops. It repeatedly calls a module (or another project) until/while its result table is not empty, or empty, depending on the settings.


Use cases

The action can be used in various cases, for instance:

  • Obtaining data from REST APIs with data pagination (See Community example)
  • Polling a web API until an external task is complete
  • Waiting until a file appears in a folder
  • Dealing with parent-child data structures (See Community example)
  • Repeatedly apply the same calculation to a dataset until it no longer changes


Action settings

SettingDescription
Module/Project to run*Select whether to call a module (within the current project), or an external project (.morph file), then select the
module, or browse to the project file.
Result tableSelect the table in the called module (or projet) that will be returned to the calling Repeat action.
RepeatSelect whether the Repeat loop with stop once the result table is empty, or finally contains data. Options: UNTIL result table is empty or WHILE result table is empty.
ModeSelect the appropriate options for handling the return of results, and the timing of loops. See the Mode settings table, below.
Fail if number of iterations exceeds*Enter a value to represent the maximum number of loops the Repeat will perform before failing. This prevents malformed Repeat actions from running infinite loops by stopping at a pre-defined point.
Assign parametersIf values will be passed into the called module/project via parameters, select the name(s) of parameter(s) to assign,
and enter the value* being passed in.

* Setting can be specified using a parameter.

Mode settings

Setting Description
Don't return resultSelect this when a returned dataset is not required in the calling workflow.
UNTIL result table is empty loops
Return the last not empty resultSelect to return the last non-empty dataset before workflow iterations produced an empty table.
Append and return all resultsSelect this to continually append the results from all iterations and return the accumulated results.
WHILE result table is empty loops
Return the first not empty resultSelect to return the first non-empty dataset once the module's (or project's) criteria have been met.
Delay between iterationsCheck this setting to insert a delay between loops and enter the number of seconds* to delay.

* Setting can be specified using a parameter.


Remarks

If the called module contains the Input action, the first iteration is populated with the input dataset of the Repeat action that calls it. In the following iterations, it's populated with the result dataset from the previous iterations. In other words, the result of an iteration is automatically passed as the input to the next iteration.

When using the Input action in the called module, you can use the "Populate automatically" button to import the current dataset from the calling module to use as test data to build the rest of the module with.

You may need to balance the "Delay…" and "Fail after…" settings so your workflow succeeds or fails within an acceptable period of time.


Examples

Objective: Set up a process that waits for a file to appear in a "watched" folder before proceeding.

Module 1 ("Main"): Set up a Repeat action to call Module 2 (below).

Action parameters:

Module to run is "WatchFolder"
Result table is "Return filenames in Watched Folder"
Repeat "WHILE result table is empty" (waiting for a file to appear in an empty folder)
Mode is "Return the first not empty result" (return the file name)
Delay is "unchecked" (no delay between iterations)
Fail if the number of iterations exceeds "1000"
There are no parameters in this example.


Module 2 ("WatchFolder"): Set up a List of files action pointing to the watched folder.

Action parameters:

Folder is the full path to the watched folder
Columns is simply "File name with full path"


The Repeat will continue to call the "WatchFolder" module until the List of files action returns a file name - which will occur when a file appears in the folder.

If a file does not appear in the target folder before Repeat has run 1000 iterations, the Repeat will fail with an error.


Community examples


See also

transformations/repeat.1626579487.txt.gz · Last modified: 2021/07/17 23:38 by craigt