Export Excel based on attribute

I have an entity called ‘Klant’ , an entity called ‘Contract’ and an entity called ‘Aansluiting’ One customer can have multiple Contracten. One contract can have multiple Aansluitingen. I made a export to excell. That works fine. The excel sheet show me all the ‘Klanten’  with their ‘Contracten’ and the ‘Aansluitingen’ per contract. But…. a contract is of isn't signed. Therefore I have an attribute called ‘DatumOndertekening’ (SignDate). What I want is to only show those contracts (with the Aansluitingen belonging to those contracts), which are signed. If the ‘DatumOndertekening’ is empty, I don't want to see those contracts (with the Aansluitingen belonging to those contracts) in the excell sheet.   I tried a lot. My basis Microflow looks like this:  I tried to make an extra retrieve after the Loop, retrieving a list of Contracts. Sort them by date and an Xpath to exclude those objects with no value to the attribute DatumOndertekening. I tried more options, but so far, nothing worked. Who could help me out?
1 answers

I solved it my self. Not by changing the microflow, but you can make it in the excel template. 

Go to Constraints:


add a new constraint:


This solved my issue. I won't remove my question, because others might have the same problem.