Using expressions in custom data flow transformation

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Using expressions in custom data flow transformation

Hi,

I'm creating a custom data flow transformation in c#.

I would like to use expressions within this component in the same way as in the derived column component: specifying the expression as a custom property of an output column, then evaluating this expression for each row of the buffer and using this evaluated expression to populate my output column values.

So I've added an custom expression on my output column, and set its expression type to CPET_NOTIFY

IDTSCustomProperty90 exp = col.CustomPropertyCollection.New();

exp.Name = "Expression";

exp.ExpressionType = DTSCustomPropertyExpressionType.CPET_NOTIFY;

But in the ProcessInput method I don't manage to get the evaluated expressions, when I use exp.Value I get my expression definition and not its evaluation.

Is there a way to get these evaluated expressions

Thanks,

Stephane

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Using expressions in custom data flow transformation

  • gqlu

    spattewar wrote:

    Hi Stephane,

    Is it possible for your to share your code with me I am also trying to create a custom data flow transformation. I am pretty new to this and have no idea on how to progress with this.

    Thanks for your time.

    $wapnil

    spattewar@gmail.com



    Stephane posted about expressions. Mark said it wouldn't work. Are you looking simply for examples, or are you looking for code that doesn't work


  • sapo

  • Milo123

    Hi Stephane,

    Is it possible for your to share your code with me I am also trying to create a custom data flow transformation. I am pretty new to this and have no idea on how to progress with this.

    Thanks for your time.

    $wapnil

    spattewar@gmail.com

  • Donaghy

    What you are trying to do is not possible, I'm afraid. The expression evaluator capability is not exposed in the dataflow.

    The CPET_NOTIFY flag can be applied to component-level custom properties of a dataflow task. Properties marked this way get evaluated once just before the execution of the dataflow. You will not be able to do per-row expressions on columns the way Derived Column does, however.

    Thanks
    Mark



  • dzimmy

    I wanted to get the source of the custom data flow transformation that stephane was building so that I know which are the methods that I need to override or how to add input and output columns.

    Thanks.

    $wapnil
  • Using expressions in custom data flow transformation
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