You can update dynamic lookup cache based on the results of a boolean expression. The Integration Service updates the cache when the expression is true.
For example, you might have a product number, quantity on hand, and a timestamp column in a target table. You need to update the quantity on hand with the latest source values. You can update the quantity on hand when the source data has a timestamp greater than the timestamp in the dynamic cache. Create an expression in the Lookup transformation similar to the following expression:
lookup_timestamp < input_timestamp
The expression can include the lookup and the input ports. You can access built-in, mapping, and parameter variables. You can include user-defined functions and refer to unconnected transformations.
The expression returns true, false, or NULL. If the result of the expression is NULL, the expression is false. The Integration Service does not update the cache. You can add a check for NULL values in the expression if you need to change the expression result to true. The default expression value is true.
Create the expression with the Transformation Developer. You cannot override the