tWriteJSONField - 6.1

Talend Open Studio for Big Data Components Reference Guide

EnrichVersion
6.1
EnrichProdName
Talend Open Studio for Big Data
task
Data Governance
Data Quality and Preparation
Design and Development
EnrichPlatform
Talend Studio

Function

tWriteJSONField transforms the incoming data into JSON fields.

Purpose

tWriteJSONField transforms the incoming data into JSON fields and transfers them to a file, a database table, etc.

Configuring a JSON Tree

When configuring a JSON tree, the default type of an element is string. If an element is not of type string, you need to add an attribute for the element to set its type.

  • For an integer, double, float, or boolean element, you need to add an attribute named type and set its static value to integer, number, float, or boolean respectively.

  • For an array element, you need to add an attribute named class and set its static value to array, and then add a sub-element named element set as a loop.

  • For an object element, you need to add an attribute named class and set its static value to object.

The following figure shows an example of JSON tree configuration:

tWriteJSONField properties

Component family

Processing/Fields

 

Basic settings

Output Column

List of the columns defined in the output schema to hold the JSON field generated.

 

Configure JSON Tree

Opens the interface to create the JSON data structure. For more information, see Configuring a JSON Tree.

 

Schema and Edit Schema

A schema is a row description. It defines the number of fields (columns) to be processed and passed on to the next component. The schema is either Built-In or stored remotely in the Repository.

Click Edit schema to make changes to the schema. If the current schema is of the Repository type, three options are available:

  • View schema: choose this option to view the schema only.

  • Change to built-in property: choose this option to change the schema to Built-in for local changes.

  • Update repository connection: choose this option to change the schema stored in the repository and decide whether to propagate the changes to all the Jobs upon completion. If you just want to propagate the changes to the current Job, you can select No upon completion and choose this schema metadata again in the [Repository Content] window.

 

 

Built-In: You create and store the schema locally for this component only. Related topic: see Talend Studio User Guide.

 

 

Repository: You have already created the schema and stored it in the Repository. You can reuse it in various projects and Job designs. Related topic: see Talend Studio User Guide.

 

Sync columns

Click to synchronize the output file schema with the input file schema. The Sync function only displays once the Row connection is linked with the output component.

 

Group by

Define the aggregation set, the columns you want to use to regroup the data.

Warning

Make sure that the data to be grouped is in sequential order.

 

Remove root node

Select this check box to remove the root node from the JSON field generated.

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.

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.

NB_LINE: the number of rows read by an input component or transferred to an output component. This is an After variable and it returns an integer.

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

Preceded by an input component, this component wraps the incoming data into a JSON field.

Scenario: Writing flat data into JSON fields

In this scenario, flat data is wrapped into JSON fields via tWriteJSONField.

Linking the components

  1. Drop the following components from the Palette onto the design workspace: tFixedFlowInput, tWriteJSONField and tLogRow.

  2. Link tFixedFlowInput and tWriteJSONField using a Row > Main connection.

  3. Link tWriteJSONField and tLogRow using a Row > Main connection.

Configuring the components

  1. Double-click tFixedFlowInput to display its Basic settings view.

  2. Click Edit schema to open the schema editor.

    Click the [+] button to add three columns, namely firstname, lastname and dept, with the type of string.

    Click OK to close the editor.

  3. Select the Use Inline Content option and enter the data below in the Content box:

    Andrew;Wallace;Doc
    John;Smith;R&D
    Christian;Dior;Sales
  4. Click tWriteJSONField to display its Basic settings view.

    Select the Remove root node option to remove the root node setting from the JSON fields generated.

  5. Click Configure JSON Tree to open the XML tree editor.

    The schema of tFixedFlowInput appears in the Linker source panel.

  6. In the Linker target panel, click the default rootTag and type in staff, which is the root node of the JSON field to be generated.

  7. Right-click staff and select Add Sub-element from the context menu.

  8. In the pop-up box, enter the sub-node name, namely firstname.

    Repeat the steps to add two more sub-nodes, namely lastname and dept.

  9. Right-click firstname and select Set As Loop Element from the context menu.

  10. Drop firstname from the Linker source panel to its counterpart in the Linker target panel.

    In the pop-up dialog box, select Add linker to target node.

    Click OK to close the dialog box.

    Repeat the steps to link the two other items.

    Click OK to close the XML tree editor.

  11. Click Edit schema to open the schema editor.

  12. Click the [+] button in the right panel to add one column, namely staff, which will hold the JSON data generated.

    Click OK to close the editor.

  13. Double-click tLogRow to display its Basic settings view.

    Select Table (print values in cells of a table) for a better display of the results.

Executing the Job

  1. Press Ctrl + S to save the Job.

  2. Click F6 to execute the Job.

    As shown above, the JSON fields have been generated correctly, with the root node settings removed.