Thanks for your answer.
But the field ‘kundentyp’ (type: radio button / transl.: typ of customer) is used in user profile and ‘kundenzugang’ (type: radio button / transl.: access of customer) is used in the productcategories.
Only the field ‘soll_das_produkt_offentlich_dargestellt_werden’ (type: true/false / transl.: should the product be published?) is a field in the post.
So the query-method won’t be the right one, or am I wrong?