# Explicitly implement "modifiy" logic in RequestData method of a vtkAlgorithm Subclass?

**URL:** https://discourse.vtk.org/t/explicitly-implement-modifiy-logic-in-requestdata-method-of-a-vtkalgorithm-subclass/3797
**Category:** Support
**Created:** [July 18, 2020, 9:27am UTC](https://discourse.vtk.org/t/explicitly-implement-modifiy-logic-in-requestdata-method-of-a-vtkalgorithm-subclass/3797 "2020-07-18T09:27:01Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![jaswantp](https://discourse.vtk.org/user_avatar/discourse.vtk.org/jaswantp/32/10046_2.png) [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [July 18, 2020, 9:27am UTC](https://discourse.vtk.org/t/explicitly-implement-modifiy-logic-in-requestdata-method-of-a-vtkalgorithm-subclass/3797/1 "2020-07-18T09:27:01Z")

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When vtkAlgorithm (or) its sub-classes `vtk[UnstructuredGrid], PolyData],..]Algorithm` and the like are sub-classed, do I have to explicitly check mTime and do the processing only if it is required or is the magic all done behind the scenes in the VTK execution model? The way I understand it, this is all supposed to be hidden and taken care of in the execution pipeline in that the filter calls RequestData internally only if needed. Right? I may not be correct in the exact details, but my question is just this. _Does a developer have to check modified logic explicitly in the RequestData method?_

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### Author: ![jaswantp](https://discourse.vtk.org/user_avatar/discourse.vtk.org/jaswantp/32/10046_2.png) [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [July 18, 2020, 1:10pm UTC](https://discourse.vtk.org/t/explicitly-implement-modifiy-logic-in-requestdata-method-of-a-vtkalgorithm-subclass/3797/2 "2020-07-18T13:10:05Z")

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Ok. It appears no such action is required. VTK takes care of it.