Index: ChapterX.Infrastructure/Repositories/CollaborationRepository.cs
===================================================================
--- ChapterX.Infrastructure/Repositories/CollaborationRepository.cs	(revision 877c13c3dd0934c1d31da7988d0d2c2c5925ed55)
+++ ChapterX.Infrastructure/Repositories/CollaborationRepository.cs	(revision b373fea3e2c9d404606002f8e7ba265a82d68187)
@@ -2,9 +2,5 @@
 using ChapterX.Domain.Repositories;
 using ChapterX.Infrastructure.Data.DataContext;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
 
 namespace ChapterX.Infrastructure.Repositories
@@ -15,4 +11,18 @@
         {
         }
+
+        public override async Task<IEnumerable<Collaboration>> GetAllAsync(CancellationToken cancellationToken = default)
+            => await _dbSet
+                .Include(c => c.User)
+                .ToListAsync(cancellationToken);
+
+        public async Task<bool> DeleteByUserAndStoryAsync(int userId, int storyId, CancellationToken cancellationToken = default)
+        {
+            var collab = await _dbSet.FirstOrDefaultAsync(c => c.UserId == userId && c.StoryId == storyId, cancellationToken);
+            if (collab == null) return false;
+            _dbSet.Remove(collab);
+            await _context.SaveChangesAsync(cancellationToken);
+            return true;
+        }
     }
 }