I was glad that I found by help of this page that elasticsearch has the collapse function.
But now I have the problem why I search for collapse again.
It is the post_filter.
I want to aggragate some conditions of objects first and then filter them from the hits.
But the problem is that the post_filter doesn't work on the inner_hits, too.
Is there any possibilty to do that or will I have to do a second request to get the perfect aggregation?