Custom transformations can be used to change the default row strategy. By default, the row strategy for a Custom transformation is pass-through when the transformation scope is Row. But, not all Custom Transformations have the default row strategy as pass-through when the transformation scope is row. When the transformation scope is Transaction or All Input, the row strategy is the same value as the Treat Source Rows As session property by default.
For example, in a mapping you have an Update Strategy transformation followed by a Custom transformation with Row transformation scope. The Update Strategy transformation flags the rows for update, insert, or delete. When the Integration Service passes a row to the Custom transformation, the Custom transformation retains the flag since its row strategy is pass-through.
However, you can change the row strategy of a Custom transformation with PowerCenter using the INFA_CTChangeDefaultRowStrategy() function. For example, when you change the default row strategy of a Custom transformation to insert, the Integration Service flags all the rows that pass through this transformation for insert (Note: The Integration Service returns INFA_FAILURE if the session is not in data-driven mode).
Hence there can be scenarios where rows flagged for insert, update or delete may change after passing through the Custom transformation.
If the mapping contains an Update Strategy transformation the Treat Source Rows As session property is marked Data Driven by default.The Integration Service follows the instructions coded in a Update Strategy or Custom transformation in the mapping to determine how to flag rows (insert, delete, update, or reject). This exerts finer control over how you flag rows (for insert, delete, update, or reject). Choose this setting when rows destined for the same table need to be flagged for one operation (for example, update), or for a different operation (for example, reject) depending on the data.
If you do not choose Data Driven when a mapping contains an Update Strategy or Custom transformation, the Workflow Manager displays a warning. When you run the session, the Integration Service does not follow the instructions in the Update Strategy or Custom transformation in the mapping to determine how to flag rows.
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