add 2 new Queries and 2 Methods for UserService

src/main/java/mops/gruppen2/service/UserService.java

@@ -0,0 +1,25 @@
+package mops.gruppen2.service;
+
+import mops.gruppen2.domain.EventDTO;
+import mops.gruppen2.repository.EventRepository;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+import java.util.Optional;
+
+@Service
+public class UserService {
+
+    final EventRepository eventRepository;
+
+    public UserService(EventRepository eventRepository) {
+        this.eventRepository = eventRepository;
+    }
+
+    public List<Long> getUserGroups(Long user_id) {
+        List<Long> group_ids = eventRepository.findGroup_idsWhereUser_id(user_id);
+
+        return null;
+    }
+}