Core Data - add relationship information to existing object

i set up a core data model with a "user" entity with several attributes.

There's a second entity called "information".

A "user" can have multiple "information" objects... A "information" allways have one "user"

with these objects i initialize a tableview. the number of sections is the number of "users" the number of rows is the number of "informations" associating to a user

everything fine until now.

with the "user" attribute values i start several API Rest Requests (i do this in viewForHeaderInSection for every single user...).

now, when im getting a successful response from the API provider with the needed results i stuck associating the result with the matching "user" entity.

i created a fetchresult with predicate to get the right user - but when creating a new "information" entity and then associating the "relation property" to the fetchresult everything breaks... :(

thanks in advance