tMysqlSCD - 6.3

Talend Open Studio for Big Data Components Reference Guide

EnrichVersion
6.3
EnrichProdName
Talend Open Studio for Big Data
task
Data Governance
Data Quality and Preparation
Design and Development
EnrichPlatform
Talend Studio

Function

tMysqlSCD reflects and tracks changes in a dedicated MySQL SCD table.

Purpose

tMysqlSCD addresses Slowly Changing Dimension needs, reading regularly a source of data and logging the changes into a dedicated SCD table

tMysqlSCD Properties

Component family

Databases/MySQL

 

Basic settings

Property type

Either Built-in or Repository.

Since version 5.6, both the Built-In mode and the Repository mode are available in any of the Talend solutions.

 

 

Built-in: No property data stored centrally.

 

 

Repository: Select the Repository file where properties are stored. The following fields are pre-filled in using fetched data.

 

Use an existing connection

Select this check box and in the Component List click the relevant connection component to reuse the connection details you already defined.

Note

When a Job contains the parent Job and the child Job, if you need to share an existing connection between the two levels, for example, to share the connection created by the parent Job with the child Job, you have to:

  1. In the parent level, register the database connection to be shared in the Basic settings view of the connection component which creates that very database connection.

  2. In the child level, use a dedicated connection component to read that registered database connection.

For an example about how to share a database connection across Job levels, see Talend Studio User Guide.

 

DB Version

Select the Mysql version you are using.

 

Host

Database server IP address.

 

Port

Listening port number of DB server.

 

Database

Name of the database.

 

Username and Password

DB user authentication data.

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.

 

Table

Name of the table to be written. Note that only one table can be written at a time.

 

Action on table

On the table defined, you can perform one of the following operations:

None: No operation is carried out.

Create a table: The table does not exist and gets created.

Create a table if not exists: The table is created if it does not exist.

 

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.

Since version 5.6, both the Built-In mode and the Repository mode are available in any of the Talend solutions.

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 is 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. Related topic: see Talend Studio User Guide.

 

SCD Editor

The SCD editor helps to build and configure the data flow for slowly changing dimension outputs.

For more information, see SCD management methodologies.

 

Use memory saving mode

Select this check box to maximize system performance.

 

Source keys include Null

Select this check box to allow the source key columns to have Null values.

Warning

Special attention should be paid to the uniqueness of the source key(s) values when this option is selected.

 

Die on error

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

Advanced settings

Additional JDBC Parameters

Specify additional connection properties for the DB connection you are creating. This option is not available if you have selected the Use an existing connection check box in the Basic settings.

 

End date time details

Specify the time value of the SCD end date time setting in the format of HH:mm:ss. The default value for this field is 12:00:00.

This field appears only when SCD Type 2 is used and Fixed year value is selected for creating the SCD end date. For more information about SCD Type 2, see SCD management methodologies.

 

tStatCatcher Statistics

Select this check box to collect log data at the component level.

 

Debug mode

Select this check box to display each step during processing entries in a database.

Dynamic settings

Click the [+] button to add a row in the table and fill the Code field with a context variable to choose your database connection dynamically from multiple connections planned in your Job. This feature is useful when you need to access database tables having the same data structure but in different databases, especially when you are working in an environment where you cannot change your Job settings, for example, when your Job has to be deployed and executed independent of Talend Studio.

The Dynamic settings table is available only when the Use an existing connection check box is selected in the Basic settings view. Once a dynamic parameter is defined, the Component List box in the Basic settings view becomes unusable.

For examples on using dynamic parameters, see Scenario 3: Reading data from MySQL databases through context-based dynamic connections and Scenario: 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.

Global Variables

NB_LINE_UPDATED: the number of rows updated. This is an After variable and it returns an integer.

NB_LINE_INSERTED: the number of rows inserted. This is an After variable and it returns an integer.

NB_LINE_REJECTED: the number of rows rejected. 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 is used as Output component. It requires an Input component and Row main link as input.

SCD management methodologies

Slowly Changing Dimensions (SCDs) are dimensions that have data that slowly changes. The SCD editor offers the simplest method of building the data flow for the SCD outputs. In the SCD editor, you can map columns, select surrogate key columns, and set column change attributes through combining SCD types.

The following figure illustrates an example of the SCD editor.

SCD keys

You must choose one or more source keys columns from the incoming data to ensure its unicity.

You must set one surrogate key column in the dimension table and map it to an input column in the source table. The value of the surrogate key links a record in the source to a record in the dimension table. The editor uses this mapping to locate the record in the dimension table and to determine whether a record is new or changing. The surrogate key is typically the primary key in the source, but it can be an alternate key as long as it uniquely identifies a record and its value does not change.

Source keys: Drag one or more columns from the Unused panel to the Source keys panel to be used as the key(s) that ensure the unicity of the incoming data.

Surrogate keys: Set the column where the generated surrogate key will be stored. A surrogate key can be generated based on a method selected on the Creation list.

Creation: Select any of the below methods to be used for the key generation:

Auto increment: auto-incremental key.

Input field: key is provided in an input field.

When selected, you can drag the appropriate field from the Unused panel to the complement field.

Routine: from the complement field, you can press Ctrl+ Space to display the autocompletion list and select the appropriate routine.

Table max +1: the maximum value from the SCD table is incremented to create a surrogate key.

DB Sequence: from the complement field, you can enter the name of the existing database sequence that will automatically increment the column indicated in the name field.

Note

This option is only available through the SCD Editor of the tOracleSCD component.

Combining SCD types

The Slowly Changing Dimensions support four types of changes: Type 0 through Type 3. You can apply any of the SCD types to any column in a source table by a simple drag-and-drop operation.

Type 0: is not used frequently. Some dimension data may be overwritten and other may stay unchanged over time. This is most appropriate when no effort has been made to deal with the changing dimension issues.

Type 1: no history is kept in the database. New data overwrites old data. Use this type if tracking changes is not necessary. this is most appropriate when correcting certain typos, for example the spelling of a name.

Type2: the whole history is stored in the database. This type tracks historical data by inserting a new record in the dimensional table with a separate key each time a change is made. This is most appropriate to track updates, for example.

SCD Type 2 principle lies in the fact that a new record is added to the SCD table when changes are detected on the columns defined. Note that although several changes may be made to the same record on various columns defined as SCD Type 2, only one additional line tracks these changes in the SCD table.

The SCD schema in this type should include SCD-specific extra columns that hold standard log information such as:

-start: adds a column to your SCD schema to hold the start date. You can select one of the input schema columns as a start date in the SCD table.

-end: adds a column to your SCD schema to hold the end date value for a record. When the record is currently active, the end date is NULL or you can select Fixed Year Value and fill in a fictive year to avoid having a null value in the end date field.

-version: adds a column to your SCD schema to hold the version number of the record.

-active: adds a column to your SCD schema to hold the true or false status value. this column helps to easily spot the active record.

Type 3: only the information about a previous value of a dimension is written into the database. This type tracks changes using separate columns. This is most appropriate to track only the previous value of a changing column.

Tracking data changes using Slowly Changing Dimensions (type 0 through type 3)

This scenario describes a Job that stores and manages both the current and historical employee data in a MySQL table using SCD (Slowly Changing Dimensions).

The input data contains various employee details including name, age, role, and salary, and another id column is added to help ensuring the unicity of the input data.

At first, the following employee data is inserted to a new MySQL table using SCD:

id;name;age;role;salary
1;Mark Smith;30;tester;11000.00
2;Thomas Johnson;32;developer;12000.00
3;Teddy Brown;33;tester;13000.00

Then the table is updated using SCD with the following renewed employee data.

id;name;age;role;salary
1;Mark Smith;31;tester;11000.00
2;Thomas Johnson;32;developer;12000.00
3;Teddy Brown;33;writer;13500.00

You can see the age of Mark Smith is updated from 30 to 31, the role of Teddy Brown is changed from tester to writer, and his salary is raised from 13000.00 to 13500.00. In this scenario,

  • we don't want to track the data changes for the name field, so we will perform Type 0 SCD on it,

  • we want the new age data to overwrite the existing data, so we will perform Type 1 SCD on it,

  • we want to retain the full history of the role data, and always create a new record with the changed data and close the previous record, so we will perform Type 2 SCD on it,

  • we want to keep the current and previous dimension values for the salary field, so we will perform Type 3 SCD on it.

For more information about SCD types, see SCD management methodologies.

Creating a Job for tracking data changes in MySQL using SCD

Create a Job to open a connection to a MySQL database, insert the employee data into a MySQL database table using SCD (Slowly Changing Dimensions), retrieve and display the inserted data on the console, then update the employee data in MySQL using SCD, retrieve and display the updated data on the console, finally close the connection to the MySQL database.

  1. Create a new Job and add a tMysqlConnection component, two tFixedFlowInput components, two tMysqlSCD components, two tMysqlInput components, two tLogRow components, and a tMysqlClose component by typing their names in the design workspace or dropping them from the Palette.

  2. Link the first tFixedFlowInput component to the first tMysqlSCD component using a Row > Main connection.

  3. Do the same to link the first tMysqlInput component to the first tLogRow component, the second tFixedFlowInput component to the second tMysqlSCD component, and the second tMysqlInput component to the second tLogRow component.

  4. Link the tMysqlConnection component to the first tFixedFlowInput component using a Trigger > OnSubjobOk connection.

  5. Do the same to link the first tFixedFlowInput component to the first tMysqlInput component, the first tMysqlInput component to the second tFixedFlowInput component, the second tFixedFlowInput component to the second tMysqlInput component, and the second tMysqlInput component to the tMysqlClose component.

Opening a connection to a MySQL database

Configure the tMysqlConnection component to open a connection to a MySQL database.

  1. Double-click the tMysqlConnection component to open its Basic settings view.

  2. In the Host, Port, Database, Username, and Password fields, enter the information required for the connection to the MySQL database.

Inserting the employee data into a MySQL table using SCD

Configure the first tFixedFlowInput component and the first tMysqlSCD component to insert the employee data into a MySQL database table using SCD (Slowly Changing Dimensions).

  1. Double-click the first tFixedFlowInput component to open its Basic settings view.

  2. Click the button next to Edit schema and in the pop-up window define the schema by adding five columns: id and age of Integer type, name and role of String type, and salary of Double type.

    When done, click OK to save the changes. In the pop-up dialog box, click Yes to propagate the schema to the next component.

  3. In the Mode area, select Use Inline Content (delimited file). Then in the Content field displayed, enter the following input employee data.

    1;Mark Smith;30;tester;11000.00
    2;Thomas Johnson;32;developer;12000.00
    3;Teddy Brown;33;tester;13000.00
    
  4. Click the first tMysqlSCD component to open its Basic settings view.

  5. Select the Use an existing connection check box and from the Component List drop-down list displayed, select the connection component you have configured.

  6. In the Table field, enter the name of employee_scd.

  7. Click the button next to SCD Editor to open the SCD editor. All schema columns are listed on the Unused panel.

  8. In the name field on the Surrogate keys panel, enter the name for the surrogate key, SK in this example.

  9. From the Unused panel, drag and drop

    • id to the Source keys panel to use it as the key to ensure the unicity of the input data,

    • name to the Type 0 fields panel and no special action will be performed upon dimension changes of it,

    • age to the Type 1 fields panel to perform Type 1 SCD on it,

    • role to the Type 2 fields panel to perform Type 2 SCD on it, and

    • salary to the Type 3 fields panel to perform Type 3 SCD on it.

  10. In the Versioning panel, select the version check box to hold the version numbers for the historical and current records in the SCD table, and select also the active check box to add the column that will hold the True value for the current active record or the False value for the historical records in the SCD table.

    When done, click OK to save the changes and close the SCD editor.

Retrieving the inserted employee data from MySQL

Configure the first tMysqlInput component and the first tLogRow component to retrieve the inserted employee data from the MySQL SCD table and display it on the console.

  1. Double-click the tMysqlInput component to open its Basic settings view.

  2. Select the Use an existing connection check box and from the Component List drop-down list displayed, select the connection component you have configured.

  3. In the Table Name field, enter the name of the table from which the employee data will be retrieved. In this example, it is employee_scd.

  4. Open the schema editor of the tMysqlSCD component, select and copy all its schema columns, then open the schema editor of the tMysqlInput component, define its schema by pasting those schema columns you have copied from the tMysqlSCD component.

    When done, click OK to save the changes. In the pop-up dialog box, click Yes to propagate the schema to the next component.

  5. Click the Guess Query button to fill the Query field with the automatically generated SQL query that will extract data of all columns from the specified table.

  6. Double-click the first tLogRow component to open its Basic settings view. In the Mode area, select Table (print values in cells of a table) for better readability of the result displayed on the console.

Updating the employee data in MySQL using SCD

Configure the second tFixedFlowInput component and the second tMysqlSCD component to update the employee data in MySQL using SCD (Slowly Changing Dimensions).

  1. Double-click the second tFixedFlowInput component to open its Basic settings view.

  2. Click the button next to Edit schema and in the pop-up window define the schema by copying and pasting the schema of the first tFixedFlowInput component.

  3. In the Mode area, select Use Inline Content (delimited file). Then in the Content field displayed, enter the following updated employee data.

    1;Mark Smith;31;tester;11000.00
    2;Thomas Johnson;32;developer;12000.00
    3;Teddy Brown;33;writer;13500.00
  4. Repeat Step 4 through Step 10 in the procedure Inserting the employee data into a MySQL table using SCD to configure the second tMysqlSCD component.

Retrieving the updated employee data from MySQL

Configure the second tMysqlInput component and the second tLogRow component to retrieve the updated employee data from the MySQL SCD table and display it on the console.

  1. Repeat Step 1 through Step 5 in the procedure Retrieving the inserted employee data from MySQL to configure the second tMysqlInput component.

  2. Repeat Step 6 in the procedure Retrieving the inserted employee data from MySQL to configure the second tLogRow component.

Closing the connection to the MySQL database

Configure the tMysqlClose component to close the connection to the MySQL database.

  1. Double-click the tMysqlClose component to open its Basic settings view.

  2. From the Component List drop-down list, select the connection component that opens the connection you want to close. In this example, it is tMysqlConnection_1.

Executing the Job to track data changes in MySQL using SCD

After setting up the Job and configuring the components used in the Job for tracking data changes in MySQL using SCD, you can then execute the Job and verify the Job execution result.

  1. Press Ctrl + S to save the Job.

  2. Press F6 to execute the Job.