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Snap Type:

Read

Description:

This Snap provides the functionality of SCD (slowly changing dimension) Type 2 on a target Redshift table. The Snap executes one SQL lookup request per set of input documents to avoid making a request for every input record. Its output is typically a stream of documents for the Redshift - Bulk Upsert Snap, which updates or inserts rows into the target table. Therefore, this Snap must be connected to the Redshift - Bulk Upsert Snap to accomplish the complete SCD2 functionality.

ETL Transformations and Data Flow

This Snap enables the following ETL operations/flows:

  1. Take the incoming document from the upstream snap and perform a lookup operation in the database, producing one or two documents in the output view.
  2. If a record exists in the database (with the values provided in the input document), generate two output documents; otherwise generates only one.
  3. Feed the output documents to the Redshift Bulk Upsert Snap, which will insert them into the destination table to preserve history.

Input & Output

  • Expected upstream Snaps: Any Snap, such as a Mapper or JSON Parser Snap, whose output contains a map of key-value entries.
  • Expected downstream Snaps: Any Snap, such as the Redshift Bulk Upsert or Structure Snap, that accepts documents containing data organized as key-value pairs.
  • Input:  Each document in the input view should contain a data map of key-value entries. The input data must contain data in the Natural Key and Cause-historization fields.
  • Output: Each document in the output view contains a data map of key-value entries for all fields of a row in the target Redshift table.

Modes

Prerequisites:
  • Redshift database installed
  • Able to connect to the database from the desired plex nodes
Limitations and Known Issues:
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Configurations:

Account & Access

This Snap uses account references created on the Accounts page of SnapLogic Manager to handle access to this endpoint. See Configuring Redshift Accounts for information on setting up this type of account.

Views:

InputThis Snap has exactly one input view and expects documents in the view.
OutputThis Snap allows zero or one output views and produces documents in the view.
ErrorThis Snap has at most one error view and produces zero or more documents in the view.


Settings

Label

Required. The name for the Snap. You can modify this to be more specific, especially if you have more than one of the same Snap in your pipeline.

Schema name



The name of the database schema that contains the table whose data you want to update. Selecting a schema filters the Table name list to only show tables created in the selected schema. If you do not specify a schema in the Schema name field, the Table name field lists out all tables with the name you specify in all schemas in the database.

Default value: [None]

Note

The values can be passed using the pipeline parameters but not the upstream parameter fields.


Table name
The name of the table that contains the data you want to update.

Default value: [None]

Note

The values can be passed using the pipeline parameters but not the upstream parameter fields.


Natural key

Required. Names of fields that identify a unique row in the target table. The identity key cannot be used as the Natural key, since a current row and its historical rows cannot have the same natural key value.

Note

The values can be passed using the pipeline parameters but not the upstream parameter fields.


Example:  id (Each record has to have a unique value.)

Default value:  [None]

Cause-historization fields

Required. Names of fields where any change in values causes the historization of an existing row and the insertion of a new 'current' row.

Example: gold bullion rate

Default value:  [None]

SCD Fields

Required. Enter the field names you want to use as dimension fields–or select them from the suggestion list. The columns in the table specified in the Table name field above are used to populate the suggestion list.

Example:

 Meaning
 		 Field Value
 Current row 
 		 current_row 1
 Historical row 
 		 current_row 0
 Start date
 		 start_date $start_date
 End date end_date
 		 $end_date


Default value:
 

 Meaning
 		 Field Value
 Current row 
 		 [None] 1
 Historical row 
 		 [None] 0
 Start date
 		 [None] Date.now()
 End date [None]
 		 Date.now()
 


Ignore unchanged rows

Specifies whether the Snap must ignore writing unchanged rows from the source table to the target table. If you enable this option, the Snap generates a corresponding document in the target only if the Cause-historization column in the source row is changed. Else, the Snap does not generate any corresponding document in the target. 

Default value: Not selected

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