The Loop component allows repeated execution of a group of components or repeated processing of records.
|Component||Same input metadata||Sorted inputs||Inputs||Outputs||Each to all outputs||Java||CTL||Auto-propagated metadata|
It is highly important to manage token flow correctly. For example each token sent to the loop body must be navigated back to the Loop component. The token cannot be duplicated or cannot disappear. If these rules are not strictly followed, your jobflow processing can easily stuck in a deadlock situation.
|Input||0||Entry point for loop processing.||Any|
|1||Tokens from the loop body must be returned back to the Loop component via this port.||Any|
|Output||0||Tokens which do not satisfy While condition are sent to this port to end up the looping.||Any|
|1||Tokens which satisfy While condition are sent to this port to start loop body.||Any|
All input and output ports have arbitrary but identical metadata.
While this condition is satisfied, the iterating token is repeatedly sent to the loop body (second output port), otherwise the token is sent out of the loop (first output port).
While condition is a CTL2 expression which is evaluated against two records.
The first record ($in.0) is the token incoming from one of the input ports (either a loop initializing token or a token incoming from the loop body).
The second record ($in.1) is an artificial input for the
condition evaluator with just a single
|Logging level||no||Decides on which level token processing information should be logged.||INFO (default) | DEBUG | TRACE | OFF|
The Loop component processes records (or tokens) one by one.
The record enters the Loop component.
The record is checked to fulfill the loop condition. If the condition is not fulfilled, the record is sent out to the first output port and the processing continues from step 1 using the next record. If the condition is met, the record is sent out to the second output port.
The record is processed by components in the loop body.
The record enters the Loop component through the second input port.
Processing continues from the step 2.
All edges in loop are automatically converted to fast-propagate version. See Types of Edges.
Figure 59.3. Example of Loop component usage
This jobflow simply generates an initial token by the DataGenerator component. The Loop component applies While condition on this initial token. If the condition is not satisfied, the token is sent out of the loop. On the other hand, if the condition is satisfied, the token is sent to the loop body, where the token is processed by other components. The token must be routed back to the Loop component, where While condition is evaluated again. The token looping is performed until the condition is not satisfied. Once the token is sent out of loop, another initial token is read from the first input port.
Since CloverETL 4.0.0, Loop is also available as an ordinary Commercial Component. Up to CloverETL 4-0-0-M2, Loop was available as a Jobflow Component only.