August 16, 2023

tMysqlSCD – Docs for ESB 6.x

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tMysqlSCD

Reflects and tracks changes in a dedicated MySQL SCD table.

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

tMysqlSCD Standard properties

These properties are used to configure tMysqlSCD running in the Standard Job framework.

The Standard
tMysqlSCD component belongs to the Business Intelligence and the Databases families.

The component in this framework is generally available.

Basic settings

Property type

Either Built-in or Repository.

 

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.

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 methodology.

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.

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.

Global Variables

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

Usage rule

This component is used as Output component. It requires an Input
component and Row main link as input.

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: Reading data from 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.

SCD management methodology

Slowly Changing Dimensions (SCDs) are dimensions that change slowly over time.

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_Editor.png

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 that this option is only available through the SCD Editor of the tOracleSCD.

Slowly Changing Dimensions 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.

  • Type 2: 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.

  • 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.

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.

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:

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

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 methodology.

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)

This Job retrieves
and displays the inserted data on the console, then updates the employee data in MySQL using
SCD, retrieves and displays the updated data on the console, finally closes the connection to
the MySQL database.

mysql_scd_job.png

  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.

    mysql_scd_tmysqlconnection_basic.png

  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.

    mysql_scd_tfixedflowinput_basic.png

  2. Click the

    components-button_three_dot.png

    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.

    mysql_scd_tfixedflowinput_schema.png

    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.

  4. Click the first tMysqlSCD component to
    open its Basic settings view.

    mysql_scd_tmysqlscd_basic.png

  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

    components-button_three_dot.png

    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.

    mysql_scd_tmysqlscd_scdeditor.png

  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.

    mysql_scd_tmysqlinput_basic.png

  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.

    mysql_scd_tmysqlinput_schema.png

    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

    components-button_three_dot.png

    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.

  4. Repeat 4 through
    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 1 through
    5 in the procedure Retrieving the inserted employee data from MySQL to configure the second tMysqlInput component.
  2. Repeat 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.

    mysql_scd_result.png

    As shown above, the new age data 31 for Mark Smith
    the old age data 30, a new record with the SK value set to 4 is created for
    the role change for Teddy
    Brown     from tester to writer, and the values of the previous salary and the
    current salary for Teddy Brown are both kept in
    the newly created record.
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