feat: add /get for invitations that gets the invite and its attendees.

backend/src/main/java/online/wesal/wesal/dto/InvitationResponse.java

@@ -14,6 +14,7 @@ public class InvitationResponse {
     private TagDto tag;
     private UserDto creator;
     private LocalDateTime createdAt;
+    private java.util.List<AttendeeDto> attendees;
     
     public InvitationResponse() {}
     
@@ -97,6 +98,14 @@ public class InvitationResponse {
         this.createdAt = createdAt;
     }
     
+    public java.util.List<AttendeeDto> getAttendees() {
+        return attendees;
+    }
+    
+    public void setAttendees(java.util.List<AttendeeDto> attendees) {
+        this.attendees = attendees;
+    }
+    
     public static class TagDto {
         private Long id;
         private String name;
@@ -169,4 +178,45 @@ public class InvitationResponse {
             this.avatar = avatar;
         }
     }
+    
+    public static class AttendeeDto {
+        private Long id;
+        private String displayName;
+        private String avatar;
+        private LocalDateTime joinedAt;
+        
+        public AttendeeDto() {}
+        
+        public Long getId() {
+            return id;
+        }
+        
+        public void setId(Long id) {
+            this.id = id;
+        }
+        
+        public String getDisplayName() {
+            return displayName;
+        }
+        
+        public void setDisplayName(String displayName) {
+            this.displayName = displayName;
+        }
+        
+        public String getAvatar() {
+            return avatar;
+        }
+        
+        public void setAvatar(String avatar) {
+            this.avatar = avatar;
+        }
+        
+        public LocalDateTime getJoinedAt() {
+            return joinedAt;
+        }
+        
+        public void setJoinedAt(LocalDateTime joinedAt) {
+            this.joinedAt = joinedAt;
+        }
+    }
 }

backend/src/main/java/online/wesal/wesal/repository/AttendeeRepository.java

@@ -3,9 +3,12 @@ package online.wesal.wesal.repository;
 import online.wesal.wesal.entity.Attendee;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.stereotype.Repository;
+import java.util.List;
 
 @Repository
 public interface AttendeeRepository extends JpaRepository<Attendee, Long> {
     
     boolean existsByInvitationIdAndUserId(Long invitationId, Long userId);
+    
+    List<Attendee> findByInvitationId(Long invitationId);
 }

backend/src/main/java/online/wesal/wesal/service/InvitationService.java

@@ -59,7 +59,7 @@ public class InvitationService {
     
     public Optional<InvitationResponse> getInvitationById(Long id) {
         return invitationRepository.findById(id)
-            .map(this::mapToResponse);
+            .map(this::mapToResponseWithAttendees);
     }
     
     public List<InvitationResponse> getAvailableInvitations() {
@@ -146,4 +146,23 @@ public class InvitationService {
         
         return response;
     }
+    
+    private InvitationResponse mapToResponseWithAttendees(Invitation invitation) {
+        InvitationResponse response = mapToResponse(invitation);
+        
+        List<Attendee> attendees = attendeeRepository.findByInvitationId(invitation.getId());
+        List<InvitationResponse.AttendeeDto> attendeeDtos = attendees.stream()
+            .map(attendee -> {
+                InvitationResponse.AttendeeDto dto = new InvitationResponse.AttendeeDto();
+                dto.setId(attendee.getUser().getId());
+                dto.setDisplayName(attendee.getUser().getDisplayName());
+                dto.setAvatar(attendee.getUser().getAvatar());
+                dto.setJoinedAt(attendee.getJoinedAt());
+                return dto;
+            })
+            .collect(Collectors.toList());
+        
+        response.setAttendees(attendeeDtos);
+        return response;
+    }
 }