Expression Evaluator is mainly useful during debugging, when one wants to know the value of a particular expression at that point of debugging:

Before implementing this we generally face difficulty in computing the result of any expression at a given point of debugging. Earlier when required to find the value of a given expression during debugging, we required to try out manually using the current record values from the instance windows. In cases of complex expressions, manual calculations resulted in incorrect values in addition to time loss.

After implementing the best practice i.e. using expression evaluator, computing the values of any expression will be simpler no matter how complex the expression is and the time spent on debugging gets reduced. Below are the steps to follow.

1. While running the debugger, go to the desired transformation (Say expression)

2. Copy the desired complex expression available in the transformation (any of the ports).

3. Right click the transformation and choose expression evaluator.

4. In the editor, paste the copied expression and validate it and then click the “Evaluate” button.

6. It gives the computed value of the expression by using the current record values.


  • Evaluates the given expression against the current processing record in the transformation.
  • The same rules as in expression editor will apply over here.


  • Will be able to compute complex expressions at any point during debugging.
  • Expression Evaluator always uses the current record values from the ports of the transformation while computing the expression.
  • Manual computation is completely removed during debugging.
  • Less effort is applied for understanding what values are getting passed over a given transformation.
Posted by Muralidhar Reddy
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September 26th, 2013

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