Selection with Python in gdb Reader

You can't assign anything to parameter values with Python, you can only read them. This is because the Python code is evaluated at run-time, when the parameter values are frozen.

In this case how I can read only relationship types from gdb without reading all data?

Hi Marta, I think you may need to change the Geodatabase Reader feature type to read a specific geometry type and/or expose "Format Attributes" . Refer to this article Introduction to Working with Geodatabase Relationship Classes (safe.com) #ReadingRelationshipClasses, appears to be some attachment workspace examples there

I have tested that before I posted the question. relationship type does not have schema so feature reader is not going to help I am affraid