July 30, 2023

tPrejob – Docs for ESB 7.x

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tPrejob

Triggers a task required for the execution of a Job

tPrejob starts the execution of a
prejob.

tPrejob Standard properties

These properties are used to configure tPrejob running in the Standard Job framework.

The Standard
tPrejob component belongs to the Orchestration family.

The component in this framework is available in all Talend
products.

Global Variables

Global Variables

ERROR_MESSAGE: the error message generated by the
component when an error occurs. This is an After variable and it returns a string. This
variable functions only if the Die on error check box is
cleared, if the component has this check box.

A Flow variable functions during the execution of a component while an After variable
functions after the execution of the component.

To fill up a field or expression with a variable, press Ctrl +
Space to access the variable list and choose the variable to use from it.

For further information about variables, see
Talend Studio

User Guide.

Usage

Usage rule

tPrejob is a start component and
can only be used with an iterate connection to the next
component.

Connections

Outgoing links (from this component to another):

Trigger: On Component Ok.

Incoming links (from one component to this one):

Trigger: Synchronize; Parallelize.

For further information regarding connections, see

Talend Studio User
Guide.

For more information about the tPrejob component, see

Talend Studio User Guide.

Handling files before and after the execution of a data Job

In this scenario, a pre-job and a post-job are added to the Job describes in Finding duplicate files between two folders to handle files before and after the
execution of the main data Job.

As described in the above-mentioned scenario, when the main data Job is started, it
creates a temporary text file to store the fetched filenames. If the specified temporary
file already exists, it will be overwritten.

To prevent possible loss of data, the pre-job saves a backup copy of the specified
file by renaming it, if it exists, before the main Job is executed.

After the execution of the main data Job, the post-job deletes the temporary file
created by the data Job and restores the backup file, if any.

tPrejob_1.png

Adding and linking components

  1. With the main Job open on the design workspace, add a tPrejob, a tPostjob, a tFileDelete,
    and two tFileCopy components to the
    Job.
  2. Link the tPrejob component to the first
    tFileCopy component using a Trigger > On Component
    Ok     connection to build the pre-job.
  3. Link the tPostjob component the tFileDelete component using a Trigger > On Component
    Ok     connection, and link the tFileDelete component to the other tFileCopy component to build the post-job.
  4. Label the relevant components to better identify their roles.

Configuring the components

Configuring the pre-job

In the pre-job, the tPrejob component does
not have any parameter or property to configure; it just triggers the tFileCopy component before the execution of the main
data Job to rename the specified file, so all the required configurations are
made in the tFileCopy component.

  1. Double-click the tFileCopy component to
    show its Basic settings view.

    tPrejob_2.png

  2. Fill the File Name field with the path
    and filename of the temporary text file to be renamed, D:/temp/tempdata.csv in this example.
  3. In the Destination directory field,
    specify or browse to destination directory. In this example, we will save
    the backup copy in the same directory, D:/temp/.
  4. Select the Rename check box, and specify
    the new filename in the Destination
    filename     field, backup-tempdata.csv. Leave the other parameters as they
    are.

Configuring the post-job

In the post-job, the tPostjob component does
not have any parameter or property to configure; it just triggers the tFileDelete component after the execution of the main
data Job to delete the temporary file used to store the fetched filenames, which
then triggers the tFileCopy component to name
the backup file back to its original name.

  1. In the Basic settings view of the
    tFileDelete component, fill the
    File Name field with the path and
    filename of the temporary file to be deleted, D:/temp/tempdata.csv in this example, and leave the other
    parameters as they are.

    tPrejob_3.png

  2. Double-click the tFileCopy component to
    open its Basic settings view.

    tPrejob_4.png

  3. Fill the File Name field with the path
    and filename of the backup file, D:/temp/backup-tempdata.csv in this example.
  4. In the Destination directory field,
    specify or browse to destination directory, D:/temp/ in this example.
  5. Select the Rename check box, and specify
    the orignal name of the temporary file in the Destination filename field, tempdata.csv.
  6. Select the Remove source file check box
    to remove the backup file after the renaming action. Leave the other
    parameters as they are.

Expected execution result

If the specified temporary file exists, its data will be saved in a backup copy
before the main data Job is executed and restored thereafter.

If the temporary file does not exist, the two tFileCopy components will generate an error, but this does not
prevent the main data Job from being executed.

For the execution result of the main data Job, see Finding duplicate files between two folders.

Related scenario

For another scenario that uses the tPrejob component,
see Creating a bar chart from the input data.

Document get from Talend https://help.talend.com
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Docs 7.x
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