tExtractJSONFields

tExtractJSONFields properties

Component family	Processing/Fields
Function	tExtractJSONFields extracts the desired data from incoming JSON fields based on the XPath or JSONPath query.
Purpose	tExtractJSONFields extracts the data from JSON fields stored in a file, a database table, etc., based on the XPath or JSONPath query.
Basic settings	Property type	Either Built-in or Repository.
		Built-in: No property data is stored centrally.
		Repository: Select the repository file in which the properties are stored. The fields that follow are completed automatically using the data retrieved.
	Schema and Edit Schema	A schema is a row description, it defines the number of fields 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: The schema will be created and stored locally for this component only. Related topic: see Talend Studio User Guide.
		Repository: The schema already exists and is stored in the Repository, hence can be reused in various projects and Job designs. Related topic: see Talend Studio User Guide.
	Read By	Select a way of extracting the specified JSON field from the list, either Xpath or JsonPath.
	JSON field	List of the JSON fields to be extracted.
	Loop XPath query	Node within the JSON field, on which the loop is based. This field is available only when Xpath is selected from the Read By list.
	Loop Jsonpath query	Specify the JSONPath node on which the loop is based. This field is available only when JsonPath is selected from the Read By list.
	Mapping	Complete this table to map the columns defined in the schema to the corresponding JSON nodes. Column: The Column cells are automatically filled with the defined schema column names. XPath query: Specify the XPath node that holds the desired data. This column is available only when Xpath is selected from the Read By list. Get Nodes: Select this check box to extract the JSON data of all the nodes specified in the XPath query list or select the check box next to a specific node to extract the data of that node. This column is available only when Xpath is selected from the Read By list. Is Array: Select this check box when the JSON field to be extracted is an array instead of an object. This column is available only when Xpath is selected from the Read By list. Json query: Specify the JSONPath node that holds the desired data. For more information about JSONPath expressions, see http://goessner.net/articles/JsonPath/. This column is available only when JsonPath is selected from the Read By list.
	Die on error	Select this check box to stop the execution of the Job when an error occurs. Clear the check box to skip any rows on error and complete the process for error-free rows. When errors are skipped, you can collect the rows on error using a Row > Reject link. This feature is not available to the Storm version of this component.
Advanced settings	Encoding	Select the encoding from the list or select Custom and define it manually. This field is compulsory for database data handling.
	tStatCatcher Statistics	Select this check box to gather the Job processing metadata at a Job level as well as at each component level. Note that this check box is not available in both of the Map/Reduce version and the Storm version of the component.
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	This component is an intermediate component. It needs an input and an output components.
Usage in Map/Reduce Jobs	If you have subscribed to one of the Talend solutions with Big Data, you can also use this component as a Map/Reduce component. In a Talend Map/Reduce Job, this component is used as an intermediate step and other components used along with it must be Map/Reduce components, too. They generate native Map/Reduce code that can be executed directly in Hadoop. You need to use the Hadoop Configuration tab in the Run view to define the connection to a given Hadoop distribution for the whole Job. For further information about a Talend Map/Reduce Job, see the sections describing how to create, convert and configure a Talend Map/Reduce Job of the Talend Big Data Getting Started Guide. Note that in this documentation, unless otherwise explicitly stated, a scenario presents only Standard Jobs, that is to say traditional Talend data integration Jobs, and non Map/Reduce Jobs.
Usage in Storm Jobs	If you have subscribed to one of the Talend solutions with Big Data, you can also use this component as a Storm component. In a Talend Storm Job, this component is used as an intermediate step and other components used along with it must be Storm components, too. They generate native Storm code that can be executed directly in a Storm system. The Storm version does not support the use of the global variables. You need to use the Storm Configuration tab in the Run view to define the connection to a given Storm system for the whole Job. This connection is effective on a per-Job basis. For further information about a Talend Storm Job, see the sections describing how to create and configure a Talend Storm Job of the Talend Big Data Getting Started Guide. Note that in this documentation, unless otherwise explicitly stated, a scenario presents only Standard Jobs, that is to say traditional Talend data integration Jobs.
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	Due to license incompatibility, one or more JARs required to use this component are not provided. You can install the missing JARs for this particular component by clicking the Install button on the Component tab view. You can also find out and add all missing JARs easily on the Modules tab in the Integration perspective of your studio. For details, see https://help.talend.com/display/KB/How+to+install+external+modules+in+the+Talend+products or the section describing how to configure the Studio in the Talend Installation and Upgrade Guide.

Scenario 1: Retrieving error messages while extracting data from JSON fields

In this scenario, tWriteJSONField wraps the incoming
data into JSON fields, data of which is then extracted by tExtractJSONFields. Meanwhile, the error messages generated due to
extraction failure, which include the concerned JSON fields and errors, are retrieved
via a Row > Reject
link.

Linking the components

Drop the following components from the Palette onto the design workspace: tFixedFlowInput, tWriteJSONField, tExtractJSONFields, and tLogRow (X2). The two tLogRow components are renamed as data_extracted and reject_info.
Link tFixedFlowInput and tWriteJSONField using a Row > Main connection.
Link tWriteJSONField and tExtractJSONFields using a Row > Main connection.
Link tExtractJSONFields and data_extracted using a Row > Main connection.
Link tExtractJSONFields and reject_info using a Row > Reject connection.

Configuring the components

Setting up the tFixedFlowInput

Double-click tFixedFlowInput to display
its Basic settings view.
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.
Select Use Inline Content and enter the
data below in the Content box:

Andrew;Wallace;Doc John;Smith;R&D Christian;Dior;Sales

1
2
3

Andrew;Wallace;Doc
John;Smith;R&D
Christian;Dior;Sales

Setting up the tWriteJSONField

Click tWriteJSONField to display its
Basic settings view.
Click Configure JSON Tree to open the XML
tree editor.

The schema of tFixedFlowInput appears in
the Linker source panel.
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.
Right-click staff and select Add Sub-element from the context menu.
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.
Right-click firstname and select
Set As Loop Element from the context
menu.
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.
Click Edit schema to open the schema
editor.
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.

Setting up the tExtractJSONFields

Double-click tExtractJSONFields to
display its Basic settings view.
Click Edit schema to open the schema
editor.
Click the [+] button in the right panel
to add three columns, namely firstname,
lastname and dept, which will hold the data of their counterpart nodes in
the JSON field staff.

Click OK to close the editor.
In the pop-up Propagate box, click
Yes to propagate the schema to the
subsequent components.
In the Loop XPath query field, enter
“/staff”, which is the root node of
the JSON data.
In the Mapping area, type in the node
name of the JSON data under the XPath query
part. The data of those nodes will be extracted and passed to their
counterpart columns defined in the output schema.
Specifically, define the XPath query “firstname” for the column firstname, “lastname” for
the column lastname, and “” for the column dept. Note that “” is not
a valid XPath query and will lead to execution errors.

Setting up the tLogRow components

Double-click data_extracted to display
its Basic settings view.
Select Table (print values in cells of a
table) for a better display of the results.
Perform the same setup on the other tLogRow component, namely reject_info.

Executing the Job

Press Ctrl + S to save the Job.
Click F6 to execute the Job.

As shown above, the reject row offers such details as the data extracted,
the JSON fields whose data is not extracted and the cause of the extraction
failure.

Scenario 2: Collecting data from your favorite online social network

In this scenario, tFileInputJSON retrieves the
friends node from a JSON file that contains the
data of a Facebook user and tExtractJSONFields extracts
the data from the friends node for flat data
output.

Linking the components

Drop the following components from the Palette onto the design workspace: tFileInputJSON, tExtractJSONFields and tLogRow.
Link tFileInputJSON and tExtractJSONFields using a Row > Main connection.
Link tExtractJSONFields and tLogRow using a Row > Main connection.

Configuring the components

Double-click tFileInputJSON to display
its Basic settings view.
Click Edit schema to open the schema
editor.

Click the [+] button to add one column,
namely friends, of the String
type.

Click OK to close the editor.

Click the […] button to browse for the
JSON file, facebook.json in this
case:

{ "user": { "id": "9999912398",
            "name": "Kelly Clarkson",
            "friends": [
                 { "name": "Tom Cruise",
                   "id": "55555555555555",
                   "likes": {
                       "data": [
                            { "category": "Movie",
                              "name": "The Shawshank Redemption",
                              "id": "103636093053996",
                              "created_time": "2012-11-20T15:52:07+0000"
                            },
                            { "category": "Community",
                              "name": "Positiveretribution",
                              "id": "471389562899413",
                              "created_time": "2012-12-16T21:13:26+0000"
                            }
                                ]
                            }
                 },
                 { "name": "Tom Hanks",
                   "id": "88888888888888"
                   "likes": {
                        "data": [
                            { "category": "Journalist",
                              "name": "Janelle Wang",
                              "id": "136009823148851",
                              "created_time": "2013-01-01T08:22:17+0000"
                            },
                            { "category": "Tv show",
                              "name": "Now With Alex Wagner",
                              "id": "305948749433410",
                              "created_time": "2012-11-20T06:14:10+0000"
                            }
                            ]
                           }
                  }
                        ]
          }
}

{ "user": { "id": "9999912398",

"name": "Kelly Clarkson",

"friends": [

{ "name": "Tom Cruise",

"id": "55555555555555",

"likes": {

"data": [

{ "category": "Movie",

"name": "The Shawshank Redemption",

"id": "103636093053996",

"created_time": "2012-11-20T15:52:07+0000"

{ "category": "Community",

"name": "Positiveretribution",

"id": "471389562899413",

"created_time": "2012-12-16T21:13:26+0000"

}

]

}

{ "name": "Tom Hanks",

"id": "88888888888888"

"likes": {

"data": [

{ "category": "Journalist",

"name": "Janelle Wang",

"id": "136009823148851",

"created_time": "2013-01-01T08:22:17+0000"

{ "category": "Tv show",

"name": "Now With Alex Wagner",

"id": "305948749433410",

"created_time": "2012-11-20T06:14:10+0000"

}

]

}

]

}

Clear the Read by XPath check box.

In the Mapping table, enter the JSONPath
query “$.user.friends[*]” next to the
friends column, retrieving the entire
friends node from the source
file.
Double-click tExtractJSONFields to
display its Basic settings view.
Click Edit schema to open the schema
editor.
Click the [+] button in the right panel
to add five columns, namely id, name, like_id, like_name and
like_category, which will hold the
data of relevant nodes in the JSON field friends.

Click OK to close the editor.
In the pop-up Propagate box, click
Yes to propagate the schema to the
subsequent components.
In the Loop XPath query field, enter
“/likes/data”.
In the Mapping area, type in the queries
of the JSON nodes in the XPath query
column. The data of those nodes will be extracted and passed to their
counterpart columns defined in the output schema.
Specifically, define the XPath query “../../id” (querying the “/friends/id” node) for the column id, “../../name”
(querying the “/friends/name” node) for
the column name, “id” for the column like_id, “name” for the
column like_name, and “category” for the column like_category.
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

Press Ctrl + S to save the Job.
Click F6 to execute the Job.

As shown above, the friends data of the Facebook user Kelly Clarkson is
extracted correctly.

Document get from Talend https://help.talend.com

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Docs 5.x

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tExtractJSONFields – Docs for ESB 5.x