August 17, 2023

tMysqlSCD – Docs for ESB 5.x

tMysqlSCD

tMysqlSCD_icon32_white.png

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 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 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_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

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.

Use_Case_tMysqlSCD.png

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.

    Use_Case_tMysqlSCD1.png

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.

    Use_Case_tMysqlSCD2.png
  2. In the design workspace, double-click tFileInputDelimited to display its Basic settings view.

    Use_Case_tMysqlSCD3.png
  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.

    Use_Case_tMysqlSCD4.png
  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.

    Use_Case_tMysqlSCD5.png
  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.

    Use_Case_tMysqlSCD6.png

    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.

    Use_Case_tMysqlSCD11.png
  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.

    Use_Case_tMysqlSCD8.png

    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.

Use_Case_tMysqlSCD9.png

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.

SCD_Result.png

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