SPMS.Application/Services/TagService.cs

@@ -1,3 +1,4 @@
+using System.Text.Json;
 using SPMS.Application.DTOs.Notice;
 using SPMS.Application.DTOs.Tag;
 using SPMS.Application.Interfaces;
@@ -136,7 +137,30 @@ public class TagService : ITagService
         if (tag == null)
             throw new SpmsException(ErrorCodes.TagNotFound, "태그를 찾을 수 없습니다.", 404);
 
+        // 트랜잭션으로 원자성 보장 (태그 삭제 + 디바이스 orphan 참조 제거)
+        using var tx = await _unitOfWork.BeginTransactionAsync();
+        try
+        {
+            // 해당 태그를 참조하는 디바이스의 Tags에서 tagId 제거
+            var devices = await _deviceRepository.GetDevicesByTagIdAsync(request.TagId);
+            foreach (var device in devices)
+            {
+                var tagList = JsonSerializer.Deserialize<List<int>>(device.Tags!) ?? new();
+                tagList.Remove((int)request.TagId);
+                device.Tags = tagList.Count > 0 ? JsonSerializer.Serialize(tagList) : null;
+                device.UpdatedAt = DateTime.UtcNow;
+                _deviceRepository.Update(device);
+            }
+
             _tagRepository.Delete(tag);
+
             await _unitOfWork.SaveChangesAsync();
+            await _unitOfWork.CommitTransactionAsync();
+        }
+        catch
+        {
+            await _unitOfWork.RollbackTransactionAsync();
+            throw;
+        }
     }
 }

SPMS.Domain/Interfaces/IDeviceRepository.cs

@@ -20,4 +20,5 @@ public interface IDeviceRepository : IRepository<Device>
         bool? isActive = null, List<int>? tags = null,
         string? keyword = null, bool? marketingAgreed = null);
     Task<Dictionary<long, int>> GetDeviceCountsByTagIdsAsync(IEnumerable<long> tagIds);
+    Task<IReadOnlyList<Device>> GetDevicesByTagIdAsync(long tagId);
 }

SPMS.Infrastructure/Persistence/Repositories/DeviceRepository.cs

@@ -129,6 +129,14 @@ public class DeviceRepository : Repository<Device>, IDeviceRepository
             .ToListAsync();
     }
 
+    public async Task<IReadOnlyList<Device>> GetDevicesByTagIdAsync(long tagId)
+    {
+        var tagStr = tagId.ToString();
+        return await _dbSet
+            .Where(d => d.Tags != null && EF.Functions.Like(d.Tags, $"%{tagStr}%"))
+            .ToListAsync();
+    }
+
     public async Task<Dictionary<long, int>> GetDeviceCountsByTagIdsAsync(IEnumerable<long> tagIds)
     {
         var tagIdList = tagIds.ToList();