tCassandraInput

Function	tCassandraInput allows you to read data from a Cassandra keyspace and send data in the Talend flow.
Purpose	tCassandraInput allows you to extract the desired data from a standard or super column family of a Cassandra keyspace so as to apply changes to the data.

Mapping tables between Cassandra type and Talend data type

The first of the following two tables presents the mapping relationships between Cassandra type with Cassandra's new API, Datastax and Talend data type .

If the Cassandra version you are using with the Studio is older than 2.0, or if you select the Hector API in the component to use with Cassandra 2.0, see the second table.

Cassandra Type	Talend Data Type
Ascii	String; Character
BigInt	Long
Blob	Byte[]
Boolean	Boolean
Counter	Long
Inet	Object
Int	Integer; Short; Byte
List	List
Map	Object
Set	Object
Text	String; Character
Timestamp	Date
UUID	String
TimeUUID	String
VarChar	String; Character
VarInt	Object
Boolean	Boolean
Float	Float
Double	Double
Decimal	BigDecimal

The following table presents the mapping relationships between Cassandra type with the Hector API and Talend data type.

Cassandra Type	Talend Data Type
BytesType	byte[]
AsciiType	String
UTF8Type	String
IntegerType	Object
Int32Type	Integer
LongType	Long
UUIDType	String
TimeUUIDType	String
DateType	Date
BooleanType	Boolean
FloatType	Float
DoubleType	Double
DecimalType	BigDecimal

tCassandraInput properties

Component family	Big Data / Cassandra
Basic settings	Property type	Either Built-In or Repository. Built-In: No property data stored centrally. Repository: Select the repository file where the properties are stored.
	Use existing connection	Select this check box and in the Component List click the relevant connection component to reuse the connection details you already defined.
	DB Version	Select the Cassandra version you are using.
	API type	This drop-down list is displayed only when you have selected the 2.0 version of Cassandra from the DB version list. From this API type list, you can either select Datastax to use CQL 3 (Cassandra Query Language) with Cassandra, or select Hector to use CQL 2. Note that the Hector API is deprecated for the 2.0 or later version of Cassandra, but it is still available for use in the Studio so that you can be flexible about the version of the query language to be used with Cassandra 2.0.0. Along with the evolution of the CQL commands, the parameters to be set in the Basic settings view varies.
	Host	Hostname or IP address of the Cassandra server.
	Port	Listening port number of the Cassandra server.
	Required authentication	Select this check box to provide credentials for the Cassandra authentication. This check box appears only if you do not select the Use existing connection check box.
	Username	Fill in this field with the username for the Cassandra authentication.
	Password	Fill in this field with the password for the Cassandra authentication. To enter the password, click the [...] button next to the password field, and then in the pop-up dialog box enter the password between double quotes and click OK to save the settings.
Keyspace configuration	Keyspace	Type in the name of the keyspace from which you want to read data.
Column family configuration	Column family	Type in the name of the column family from which you want to read data.
	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.
	Query	Enter the query statements to be used to read data from the Cassandra database. By default, the query is not case-sensitive. This means that at runtime, the column names you put in the query are always taken in lower case. If you need to make the query case-sensitive, put the column names in double quotation marks. The [...] button next to this field allows you to generate the sample code that shows what the pre-defined variables are for the data to be read and how these variables can be used. This feature is available only for the Datastax API of Cassandra 2.0 or a later version.
These features are available to the Hector API only.	Column family type	Standard: Column family is of standard type. Super: Column family is of super type.
	Include key in output columns	Select this check box to include the key of the column family in output columns. Key column: select the key column from the list.
	Row key type	Select the appropriate Talend data type for the row key from the list.
	Row key Cassandra type	Select the corresponding Cassandra type for the row key from the list. Warning The value of the Default option varies with the selected row key type. For example, if you select String from the Row key type list, the value of the Default option will be UTF8. For more information about the mapping table between Cassandra type and Talend data type, see Mapping tables between Cassandra type and Talend data type.
	Include super key output columns	Select this check box to include the super key of the column family in output columns. Super key column: select the desired super key column from the list. This check box appears only if you select Super from the Column family type drop-down list.
	Super column type	Select the type of the super column from the list.
	Super column Cassandra type	Select the corresponding Cassandra type for the super column from the list. For more information about the mapping table between Cassandra type and Talend data type, see Mapping tables between Cassandra type and Talend data type.
	Specify row keys	Select this check box to specify the row keys of the column family directly.
	Row Keys	Type in the specific row keys of the column family in the correct format depending on the row key type. This field appears only if you select the Specify row keys check box.
	Key start	Type in the start row key of the correct data type.
	Key end	Type in the end row key of the correct data type.
	Key limit	Type in the number of rows to be read between the start row key and the end row key.
	Specify columns	Select this check box to specify the column names of the column family directly.
	Columns	Type in the specific column names of the column family in the correct format depending on the column type. This field appears only if you select the Specify columns check box.
	Columns range start	Type in the start column name of the correct data type.
	Columns range end	Type in the end column name of the correct data type.
	Columns range limit	Type in the number of columns to be read between the start column and the end column.
Advanced settings	tStatCatcher Statistics	Select this check box to gather the Job processing metadata at the Job level as well as at each component level.
Global Variables	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. 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 always needs an output link.
Log4j	If you are using a subscription-based version of the Studio, 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	n/a

Scenario: Handling data with Cassandra

This scenario describes a simple Job that reads the employee data from a CSV file, writes the data to a Cassandra keyspace, then extracts the personal information of some employees and displays the information on the console.

This scenario requires six components, which are:

tCassandraConnection: opens a connection to the Cassandra server.
tFileInputDelimited: reads the input file, defines the data structure and sends it to the next component.
tCassandraOutput: writes the data it receives from the preceding component into a Cassandra keyspace.
tCassandraInput: reads the data from the Cassandra keyspace.
tLogRow: displays the data it receives from the preceding component on the console.
tCassandraClose: closes the connection to the Cassandra server.

Dropping and linking the components

Drop the following components from the Palette onto the design workspace: tCassandraConnection, tFileInputDelimited, tCassandraOutput, tCassandraInput, tLogRow and tCassandraClose.
Connect tFileInputDelimited to tCassandraOutput using a Row > Main link.
Do the same to connect tCassandraInput to tLogRow.
Connect tCassandraConnection to tFileInputDelimited using a Trigger > OnSubjobOk link.
Do the same to connect tFileInputDelimited to tCassandraInput and tCassandraInput to tCassandraClose.
Label the components to better identify their functions.

Configuring the components

Opening a Cassandra connection

Double-click the tCassandraConnection component to open its Basic settings view in theComponent tab.
Select the Cassandra version that you are using from the DB Version list. In this example, it is Cassandra 1.1.2.
In the Server field, type in the hostname or IP address of the Cassandra server. In this example, it is localhost.
In the Port field, type in the listening port number of the Cassandra server.
If required, type in the authentication information for the Cassandra connection: Username and Password.

Reading the input data

Double-click the tFileInputDelimited component to open its Component view.
Click the [...] button next to the File Name/Stream field to browse to the file that you want to read data from. In this scenario, the directory is D:/Input/Employees.csv. The CSV file contains four columns: id, age, name and ManagerID.
```
id;age;name;ManagerID
1;20;Alex;1
2;40;Peter;1
3;25;Mark;1
4;26;Michael;1
5;30;Christophe;2
6;26;Stephane;3
7;37;Cedric;3
8;52;Bill;4
9;43;Jack;2
10;28;Andrews;4
```
In the Header field, enter 1 so that the first row in the CSV file will be skipped.
Click Edit schema to define the data to pass on to the tCassandraOutput component.

Writing data to a Cassandra keyspace

Double-click the tCassandraOutput component to open its Basic settings view in the Component tab.
Type in required information for the connection or use the existing connection you have configured before. In this scenario, the Use existing connection check box is selected.
In the Keyspace configuration area, type in the name of the keyspace: Employee in this example, and select Drop keyspace if exists and create from the Action on keyspace list.
In the Column family configuration area, type in the name of the column family: Employee_Info in this example, and select Drop column family if exists and create from the Action on column family list.
The Define column family structure check box appears. In this example, clear this check box.
In the Action on data list, select the action you want to carry on, Upsert in this example.
Click Sync columns to retrieve the schema from the preceding component.
Select the key column of the column family from the Key column list. In this example, it is id.
If needed, select the Include key in columns check box.

Reading data from the Cassandra keyspace

Double-click the tCassandraInput component to open its Component view.
Type in required information for the connection or use the existing connection you have configured before. In this scenario, the Use existing connection check box is selected.
In the Keyspace configuration area, type in the name of the keyspace: Employee in this example.
In the Column family configuration area, type in the name of the column family: Employee_Info in this example.
Select Edit schema to define the data structure to be read from the Cassandra keyspace. In this example, three columns id, name and age are defined.
If needed, select the Include key in output columns check box, and then select the key column of the column family you want to include from the Key column list.
From the Row key type list, select Integer because id is of integer type in this example.
Keep the Default option for the row key Cassandra type because its value will become the corresponding Cassandra type Int32 automatically.
In the Query configuration area, select the Specify row keys check box and specify the row keys directly. In this example, three rows will be read. Next, select the Specify columns check box and specify the column names of the column family directly. This scenario will read three columns from the keyspace: id, name and age.
If needed, the Key start and the Key end fields allow you to define the range of rows, and the Key limit field allows you to specify the number of rows within the range of rows to be read. Similarly, the Columns range start and the Columns range end fields allow you to define the range of columns of the column family, and the Columns range limit field allows you to specify the number of columns within the range of columns to be read.

Displaying the information of interest

Double-click the tLogRow component to open its Component view.
In the Mode area, select Table (print values in cells of a table).

Closing the Cassandra connection

Double-click the tCassandraClose component to open its Component view.
Select the connection to be closed from the Component List.

Saving and executing the Job

Press Ctrl+S to save your Job.
Execute the Job by pressing F6 or clicking Run on the Run tab.
The personal information of three employees is displayed on the console.

tCassandraInput - 6.3