tContextLoad

Loads 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.

tContextLoad modifies dynamically the values of
the active context.

tContextLoad Standard properties

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

The Standard
tContextLoad component belongs to the Misc family.

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

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

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

Global Variables

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.

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

Usage rule	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.
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 examples on using dynamic parameters, see Reading data from databases through context-based dynamic connections and Reading data from different MySQL databases using dynamically loaded connection parameters. For more information on Dynamic settings and context variables, see Talend Studio User Guide.
Limitation	tContextLoad does not create any non-defined variable in the default context.

Usage rule

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.

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 examples on using dynamic parameters, see Reading data from databases through context-based dynamic connections and Reading data from different MySQL databases using dynamically loaded connection parameters. For more information on Dynamic
settings and context variables, see Talend Studio
User Guide.

Limitation

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

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

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

Preparing the contexts and context variables

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:

host;localhost port;3306 database;test username;root password;talend

1
2
3
4
5

host;localhost
port;3306
database;test
username;root
password;talend
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.
Click the Contexts tab and click the [+] button at the upper right corner of the panel to open the
Configure Contexts dialog box.
Select the default context, click the Edit button
and rename the context to Test.
Click New to add a new context named Production. Then click OK to
close the dialog box.
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.
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.
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.

Configuring the components

In the tFileInputDelimited component Basic settings panel, fill the File
name/Stream field with the relevant context variable we just defined:
context.filename.
Define the file schema manually (Built-in). It contains two columns defined as:
key and value.
Accept the defined schema to be propagated to the next component (tContextLoad).
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.
Then double-click to open the tMysqlInput component
Basic settings view.
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.
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).
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.
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

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.

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.

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

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

Thank you for watching.

Docs 7.x

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tContextLoad – Docs for ESB 7.x