tMysqlSCD - 6.1

Talend Components Reference Guide

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6.1
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Talend Studio

tMysqlSCD Properties

Component family

Databases/MySQL

 

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

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.

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

This five-component Java scenario describes a Job that tracks changes in four of the columns in a source delimited file, writes changes and the history of changes in an SCD table, and displays error information on the Run console.

The source delimited file contains various personal details including firstname, lastname, address, city, company, age, and status. An id column helps ensuring the unicity of the data.

We want any change in the marital status to overwrite the existing old status record. This type of change is equivalent to an SCD Type 1.

We want to insert a new record in the dimensional table with a separate key each time a person changes his/her company. This type of change is equivalent to an SCD Type 2.

We want to track only the previous city and previous address of a person. This type of change is equivalent to an SCD Type 3.

To realize this kind of scenario, it is better to divide it into three main steps: defining the main flow of the Job, setting up the SCD editor, and finally creating the relevant SCD table in the database.

Defining the main flow of the Job

  1. Drop the following components from the Palette onto the design workspace: a tMysqlConnection, a tFileInputDelimited, a tMysqlSCD, a tMysqlCommit, and two tLogRow components.

  2. Connect the tFileInputDelimited, the first tLogRow, and the tMysqlSCD using the Row Main link. This is the main flow of your Job.

  3. Connect the tMysqlConnection to the tFileInputDelimited and tMysqlSCD to tMysqlCommit using the OnComponntOk trigger.

  4. Connect the tMysqlSCD to the second tLogRow using the Row Rejects link. Two columns, errorCode and errorMessage, are added to the schema. This connection collects error information.

Configuring the DB connection and the input component

  1. In the design workspace, double-click tMysqlConnection to display its Basic settings view and set the database connection details. The tMysqlConnection component should be used to avoid setting several times the same DB connection when multiple DB components are used.

    Note

    If you have already stored the connection details locally in the Repository, drop the needed metadata item to the design workspace and the database connection detail will automatically display in the relevant fields. For more information about Metadata, see Talend Studio User Guide.

    In this scenario, we want to connect to the SCD table where changes in the source delimited file will be tracked down.

  2. In the design workspace, double-click tFileInputDelimited to display its Basic settings view.

  3. Click the three-dot button next to the File Name field to select the path to the source delimited file, dataset.csv in this scenario, that contains the personal details.

  4. Define the row and field separators used in the source file.

    Note

    The File Name, Row separator, and Field separators are mandatory.

  5. If needed, set Header, Footer, and Limit.

    In this scenario, set Header to 1. Footer and limit for the number of processed rows are not set.

  6. Click Edit schema to describe the data structure of the source delimited file.

    In this scenario, the source schema is made of eight columns: id, firstName, lastName, address, city, company, age, and status.

  7. Define the basic settings for the first tLogRow in order to view the content of the source file with varying attributes in cells of a table on the console before being processed through the SCD component.

Configuring tMysqlSCD and tMysqlCommit

  1. In the design workspace, click the tMysqlSCD and select the Component tab to define its basic settings.

  2. In the Basic settings view, select the Use an existing connection check box to reuse the connection details defined on the tMysqlConnection properties.

  3. In the Table field, enter the table name to be used to track changes.

  4. If needed, click Sync columns to retrieve the output data structure from the tFileInputDelimited.

  5. In the design workspace, double-click tMysqlCommit to define its basic settings.

  6. Select the relevant connection on the Component list if more than one connection exists.

  7. Define the basic settings of the second tLogRow in order to view reject information in cells of a table.

Setting up the SCD editor

  1. Double-click the tMysqlSCD component in the design workspace or click the three-dot button next to the SCD Editor in the component's Basic settings view to open the SCD editor and build the data flow for the SCD outputs.

    All the columns from the preceding component are displayed in the Unused panel of the SCD editor. All the other panels in the SCD editor are empty.

  2. From the Unused list, drop the id column to the Source keys panel to use it as the key to ensure the unicity of the incoming data.

  3. In the Surrogate keys panel, enter a name for the surrogate key in the Name field, SK1 in this scenario.

  4. From the Creation list, select the method to be used for the surrogate key generation, Auto-increment in this scenario.

  5. From the Unused list, drop the firstname and lastname columns to the Type 0 panel, changes in these two columns do not interest us.

  6. Drop the status column to the Type 1 panel. The new value will overwrite the old value.

  7. Drop the company column to the Type 2 panel. Each time a person changes his/her company, a new record will be inserted in the dimensional table with a separate key.

    In the Versioning area:

    - Define the start and end columns of your SCD table that will hold the start and end date values. The end date is null for current records until a change is detected. Then the end date gets filled in and a new record is added with no end date.

    In this scenario, we select Fixed Year Value for the end column and fill in a fictive year to avoid having a null value in the end date field.

    - Select the version check box to hold the version number of the record.

    - Select the active check box to spot the column that will hold the True or False status. True for the current active record and False for the modified record.

  8. Drop the address and city columns to the Type 3 panel to track only the information about the previous value of the address and city.

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

  9. Click OK to validate your configuration and close the SCD editor.

Creating the SCD table

  1. Click Edit schema to view the input and output data structures.

    The SCD output schema should include the SCD-specific columns defined in the SCD editor to hold standard log information.

    Note

    If you adjust any of the input schema definitions, you need to check, and reconfigure if necessary, the output flow definitions in the SCD editor to ensure that the output data structure is properly updated.

  2. In the Basic settings view of the tMysqlSCD component, select Create table if not exists from the Action on table list to avoid creating and defining the SCD table manually.

Job execution

Save your Job and press F6 to execute it.

The console shows the content of the input delimited file, and your SCD table is created in your database, containing the initial dataset.

Janet gets divorced and moves to Adelanto at 355 Golf Rd. She works at Greenwood.

Adam gets married and moves to Belmont at 2505 Alisson ct. He works at Scoop.

Martin gets a new job at Phillips and Brothers.

Update the delimited file with the above information and press F6 to run your Job.

The console shows the updated personal information and the rejected data, and the SCD table shows the history of valid changes made to the input file along with the status and version number. Because the name of Martin's new company exceeds the length of the column company defined in the schema, this change is directed to the reject flow instead of being logged in the SCD table.