Control Flow

MDL microflows support conditional branching, loops, and error handling to control the execution path of your logic.

IF / ELSE

Conditional branching executes different activities based on a boolean expression.

Basic IF

IF $Order/TotalAmount > 1000 THEN
  CHANGE $Order (DiscountApplied = true);
END IF;

IF / ELSE

IF $Customer/Email != empty THEN
  CALL MICROFLOW Sales.SUB_SendEmail (Customer = $Customer);
ELSE
  LOG WARNING 'Customer has no email address';
END IF;

Nested IF

Since MDL does not support CASE/WHEN (switch statements), use nested IF...ELSE blocks:

IF $Order/Status = 'Draft' THEN
  CHANGE $Order (Status = 'Submitted');
ELSE
  IF $Order/Status = 'Submitted' THEN
    CHANGE $Order (Status = 'Approved');
  ELSE
    IF $Order/Status = 'Approved' THEN
      CHANGE $Order (Status = 'Shipped');
    ELSE
      LOG WARNING 'Unexpected order status: ' + $Order/Status;
    END IF;
  END IF;
END IF;

Complex Conditions

Conditions support AND, OR, and parentheses:

IF $Amount > 0 AND $Customer != empty THEN
  COMMIT $Order;
END IF;

IF ($Status = 'Active' OR $Status = 'Pending') AND $IsValid = true THEN
  CALL MICROFLOW Sales.ProcessOrder (Order = $Order);
END IF;

LOOP (FOR EACH)

Iterates over each item in a list:

LOOP $Line IN $OrderLines
BEGIN
  CHANGE $Line (
    LineTotal = $Line/Quantity * $Line/UnitPrice
  );
  COMMIT $Line;
END LOOP;

The loop variable ($Line) is automatically declared and takes the entity type of the list.

LOOP with Nested Logic

LOOP $Order IN $PendingOrders
BEGIN
  IF $Order/TotalAmount > 0 THEN
    CHANGE $Order (Status = 'Confirmed');
    COMMIT $Order;
  ELSE
    DELETE $Order;
  END IF;
END LOOP;

BREAK and CONTINUE

Use BREAK to exit a loop early, and CONTINUE to skip to the next iteration:

LOOP $Item IN $Items
BEGIN
  IF $Item/IsInvalid = true THEN
    CONTINUE;
  END IF;

  IF $Item/Type = 'StopSignal' THEN
    BREAK;
  END IF;

  CALL MICROFLOW Sales.ProcessItem (Item = $Item);
END LOOP;

WHILE Loop

Executes a block repeatedly as long as a condition remains true:

DECLARE $Counter Integer = 0;

WHILE $Counter < 10
BEGIN
  SET $Counter = $Counter + 1;
  LOG INFO 'Iteration: ' + toString($Counter);
END WHILE;

Caution: Ensure the condition will eventually become false to avoid infinite loops.

Error Handling

ON ERROR Suffix

Error handling is applied as a suffix to individual activities. There is no TRY...CATCH block in MDL. Instead, you specify error handling behavior on specific activities.

ON ERROR CONTINUE

Ignores the error and continues to the next activity:

COMMIT $Order ON ERROR CONTINUE;

ON ERROR ROLLBACK

Rolls back the current transaction and continues:

DELETE $Order ON ERROR ROLLBACK;

ON ERROR with Handler Block

Executes a custom error handling block when the activity fails:

COMMIT $Order ON ERROR {
  LOG ERROR 'Failed to commit order: ' + $Order/OrderNumber;
  ROLLBACK $Order;
};

The handler block can contain any activities – logging, rollback, showing validation messages, etc.

Error Handling Examples

-- Continue despite retrieval failure
RETRIEVE $Config FROM Admin.SystemConfig LIMIT 1 ON ERROR CONTINUE;

-- Custom error handler for external call
$Response = CALL MICROFLOW Integration.CallExternalAPI (
  Payload = $RequestBody
) ON ERROR {
  LOG ERROR NODE 'Integration' 'External API call failed';
  SET $Response = empty;
};

-- Rollback on commit failure
COMMIT $Order WITH EVENTS ON ERROR ROLLBACK;

Note: ON ERROR is not supported on EXECUTE DATABASE QUERY activities.

Unsupported Control Flow

The following constructs are not supported in MDL and will cause parse errors:

Complete Example

CREATE MICROFLOW Sales.ACT_ProcessBatch
FOLDER 'Batch'
BEGIN
  DECLARE $Orders List of Sales.Order = empty;
  DECLARE $SuccessCount Integer = 0;
  DECLARE $ErrorCount Integer = 0;

  RETRIEVE $Orders FROM Sales.Order
    WHERE Status = 'Pending';

  LOOP $Order IN $Orders
  BEGIN
    IF $Order/TotalAmount <= 0 THEN
      LOG WARNING 'Skipping order with zero amount: ' + $Order/OrderNumber;
      CONTINUE;
    END IF;

    @caption 'Process order'
    CALL MICROFLOW Sales.SUB_ProcessSingleOrder (
      Order = $Order
    ) ON ERROR {
      LOG ERROR 'Failed to process order: ' + $Order/OrderNumber;
      SET $ErrorCount = $ErrorCount + 1;
      CONTINUE;
    };

    SET $SuccessCount = $SuccessCount + 1;
  END LOOP;

  LOG INFO 'Batch complete: ' + toString($SuccessCount) + ' processed, '
    + toString($ErrorCount) + ' errors';
END;