July 30, 2023

tMysqlSCD – Docs for ESB 7.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 available in all Talend
products.

Note: This component is a specific version of a dynamic database
connector. The properties related to database settings vary depending on your database
type selection. For more information about dynamic database connectors, see Dynamic database components.

Basic settings

Database

Select a type of database from the list and click
Apply.

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. When you create a Spark
Job, avoid the reserved word line when naming the
fields.

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 Reading data from databases through context-based dynamic connections and 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.

Limitation

This component does not support using SCD type 0 together with other
SCD types.

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.

tMysqlSCD_1.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.

    Note: The end column identifies
    active records. The surrogate ID value gets reset when the value of the end column changes. To avoid duplicated surrogate
    IDs, always make sure that the value of the end column remains unchanged in the target table.
  • 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.

tMysqlSCD_2.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.

    tMysqlSCD_3.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.

    tMysqlSCD_4.png

  2. Click the

    tMysqlSCD_5.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.

    tMysqlSCD_6.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.

    tMysqlSCD_7.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

    tMysqlSCD_5.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.

    tMysqlSCD_9.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.

    tMysqlSCD_10.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.

    tMysqlSCD_11.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

    tMysqlSCD_5.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.

    tMysqlSCD_13.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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