August 17, 2023

tContextLoad – Docs for ESB 5.x

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tContextLoad

tContextLoad.png

tContextLoad properties

Component family

Misc

  

Function

tContextLoad modifies dynamically the values of
the active context.

Purpose

tContextLoad can be used to load a context from
a flow.

This component performs also two controls. It warns when the parameters defined
in the incoming flow are not defined in the context, and the other way around, it
also warns when a context value is not initialized in the incoming flow.

But note that this does not block the processing.

Basic settings

Schema and Edit schema

A schema is a row description, it defines the fields that will be processed and
passed on to the next component.

In tContextLoad, the schema must be made of two
columns, including the parameter name and the parameter value to be loaded.

 

If a variable loaded, but not in the context

If a variable is loaded but does not appear in the context, select how the
notification must be displayed. In the shape of an Error, a warning or an information
(info).

 

If a variable in the context, but not loaded

If a variable appears in the context but is not loaded, select how the
notification must be displayed. In the shape of an Error, a warning or an information
(info).

 

Print operations

Select this check box to display the context parameters set in the Run view.

 

Disable errors

Select this check box to prevent the error from displaying.

 

Disable warnings

Select this check box to prevent the warning from displaying.

 

Disable infos

Select this check box to prevent the information from displaying.

 

Die on error

This check box is selected by default. Clear the check box to skip the row on
error and complete the process for error-free rows.

Advanced settings

tStatCatcher Statistics

Select this check box to gather the Job processing metadata at a Job level as
well as at each component level.

Dynamic settings

Click the [+] button to add a row in the table
and fill the Code field with a context variable to
turn on or off the Print operations option
dynamically at runtime.

When a dynamic parameter is defined, the corresponding Print operations option in the Basic
settings view becomes unusable.

For more information on Dynamic settings and context
variables, see Talend Studio User Guide.

Global Variables

NB_LINE: the number of rows processed. This is an After
variable and it returns an integer.

KEY_NOT_INCONTEXT: the variables are loaded but do not
appear in the context. This is an After variable and it returns a string.

KEY_NOT_LOADED: the variables not loaded but appear in
the context. This is an After variable and it returns a string.

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

This component relies on the data flow to load the context values to be used,
therefore it requires a preceding input component and thus cannot be a start
component.

Log4j

The activity of this component can be logged using the log4j feature. For more information on this feature, see Talend Studio User
Guide.

For more information on the log4j logging levels, see the Apache documentation at http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Level.html.

Limitation

tContextLoad does not create any non-defined
variable in the default context.

Scenario: Reading data from different MySQL databases using dynamically loaded connection
parameters

The Job in this scenario is made of two subjobs. The first subjob aims at dynamically
loading the context parameters from two text files, and the second subjob uses the loaded
context parameters to connect to two different databases and to display the content of an
existing database table of each of them. With the context settings in the Job, we can decide
which database to connect to and choose whether to display the set context parameters on the
console dynamically at runtime.

Dropping and linking the components

  1. Drop a tFileInputDelimited component and a
    tContextLoad component from the Palette onto the design workspace, and link them using a Row > Main connection to form
    the first subjob.

  2. Drop a tMysqlInput component and a tLogRow component onto the design workspace, and link them
    using a Row > Main
    connection to form the second subjob.

  3. Link the two subjobs using a Trigger > On Subjob Ok connection.

    Use_Case_tContextLoad1.png

Preparing the contexts and context variables

  1. Create two delimited files corresponding to the two contexts in this scenario,
    namely two databases we will access, and name them
    test_connection.txt and prod_connection.txt, which contain the database connection details for
    testing and actual production purposes respectively. Each file is made of two columns,
    containing the parameter names and the corresponding values respectively. Below is an
    example:

  2. Select the Contexts view of the Job, and click the
    [+] button at the bottom of the view to add seven
    rows in the table to define the following parameters:

    • host, String type

    • port, String type

    • database, String type

    • username, String type

    • password, Password type

    • filename, File type

    • printOperations, Boolean type

    Note that the host, port, database, username and password parameters
    correspond to the parameter names in the delimited files and are used to set up the
    desired database connection, the filename parameter
    is used to define the delimited file to read at Job execution, the printOperations parameter is used to decide whether to print
    the context parameters set by the tContextLoad
    component on the console.

  3. Click the Contexts tab and click the [+] button at the upper right corner of the panel to open the
    [Configure Contexts] dialog box.

  4. Select the default context, click the Edit button
    and rename the context to Test.

  5. Click New to add a new context named Production. Then click OK to
    close the dialog box.

    use_case-tcontextload-set_parameters_2.png

  6. Back in the Contexts tab view, define the value of
    the filename variable under each context by clicking
    in the respective Value field and browse to the
    corresponding delimited file.

  7. Select the Prompt check box next to the Value field of the filename
    variable for both contexts to show the Prompt fields
    and enter the prompt message to be displayed at the execution time.

  8. For the printOperations variable, click in the
    Value field under the Production context and select false
    from the list; click in the Value field under the
    Test context and select true from the list. Then select the Prompt check box under both contexts and enter the prompt message to be
    displayed at the execution time.

    use_case-tcontextload-set_parameters_3.png

Configuring the components

  1. In the tFileInputDelimited component Basic settings panel, fill the File
    name/Stream     field with the relevant context variable we just defined:
    context.filename.

    use_case-tcontextload-tfileinputdelimited.png

  2. Define the file schema manually (Built-in). It contains two columns defined as:
    key and value.

  3. Accept the defined schema to be propagated to the next component (tContextLoad).

  4. In the Dynamic settings view of the tContextLoad component, click the [+] button to add a row in the table, and fill the Code field with context.printOperations to use context
    variable printOperations we just defined. Note that
    the Print operations check box in the Basic settings view now becomes highlighted and
    unusable.

    use_case-tcontextload-dynamicsettings.png

  5. Then double-click to open the tMysqlInput component
    Basic settings view.

  6. Fill the Host, Port, Database, Username, and Password fields with the
    relevant variables stored in the delimited files and defined in the Contexts tab view: context.host,
    context.port, context.database,
    context.username, and context.password respectively in this
    example, and fill the Table Name field with the actual
    database table name to read data from, customers for
    both databases in this example.

    Use_Case_tContextLoad4.png

  7. Then fill in the Schema information. If you stored
    the schema in the Repository Metadata, then you can
    retrieve it by selecting Repository and the relevant
    entry in the list.

    In this example, the schema of both database tables is made of four columns:
    id (INT, 2 characters long), firstName (VARCHAR, 15 characters long), lastName (VARCHAR, 15 characters long), and city (VARCHAR, 15 characters long).

  8. In the Query field, type in the SQL query to be
    executed on the DB table specified. In this example, simply click Guess Query to retrieve all the columns of the table, which will be
    displayed on the Run tab, through the tLogRow component.

  9. In the Basic settings view of the tLogRow component, select the Table option to display data records in the form of a table.

Executing the Job

  1. Press Ctrl+S to save the Job, and press F6 to run the Job using the default context, which is Test in this use case.

    A dialog box appears to prompt you to specify the delimited file to read and decide
    whether to display the set context parameters on the console.

    Use_Case_tContextLoad5.png

    You can specify a file other than the default one if needed, and clear the Show loaded variables check box if you do not want to see the
    set context variables on the console. To run the Job using the default settings, click
    OK.

    use_case-tcontextload-run1.png

    The context parameters and content of the database table in the Test context are all displayed on the Run console.

  2. Now select the Production context and press
    F6 to launch the Job again. When the prompt dialog
    box appears, simply click OK to run the Job using the
    default settings.

    use_case-tcontextload-run2.png

    The content of the database table in the Production context is displayed on the Run console. Because the printOperations variable is set to false, the set context parameters are not displayed on the console this
    time.

Document get from Talend https://help.talend.com
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Docs 5.x
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