System.invalidoperationexception: collection was modified; enumeration operation may not execute in .net 5 api project

Question

The code is working fine at local as well as dev environment but when I published the code at stage environment I am getting below error. I am not able to understand how it happens in a staging environment only.

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
   at System.Linq.Enumerable.SelectListIterator`2.MoveNext()
   at System.Linq.Enumerable.JoinIterator[TOuter,TInner,TKey,TResult](IEnumerable`1 outer, IEnumerable`1 inner, Func`2 outerKeySelector, Func`2 innerKeySelector, Func`3 resultSelector, IEqualityComparer`1 comparer)+MoveNext()
   at System.Linq.Enumerable.JoinIterator[TOuter,TInner,TKey,TResult](IEnumerable`1 outer, IEnumerable`1 inner, Func`2 outerKeySelector, Func`2 innerKeySelector, Func`3 resultSelector, IEqualityComparer`1 comparer)+MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.EnumerablePartition`1.ToList()
   at Soulmaker.Services.VideoService.GetClientDetailAsync(Int64 id, Int64 userId)
   at Soulmaker.API.Controllers.VideoController.GetClientDetails(Int32 id) in /src/Soulmaker.API/Controllers/VideoController.cs:line 184

Here is the code I am using and getting the above error as a response after making an API request at deployed code.

public async Task<VideoDetailsResponse> GetClientDetailAsync(long id, long userId)
       {
           var video = await _context.Videos
                                 .Include(x => x.CreatedByUser)
                                 .Include(x => x.Like)
                                 .Include(x => x.PublishedByUser)
                                 .Include(x => x.ModifiedByUser)
                                 .Include(x => x.Tags)
                                 .ThenInclude(x => x.Topic)
                                 .Include(x => x.AdminTags)
                                 .ThenInclude(x => x.AdminTag)
                                 .FirstOrDefaultAsync(x => !x.IsDeleted && !x.IsHidden && x.Id == id);

           var response = _mapper.Map<VideoDetailsResponse>(video);
           response.IsLiked = video.Like.Any(x => x.UserId == userId);

           var items = (from topicId in video.Tags.Select(x => x.TopicId)
                        join tag in _context.VideoTagLink on topicId equals tag.TopicId
                        join videoItem in _context.Videos
                                           .Include(x => x.CreatedByUser)
                                           .Include(x => x.Like)
                                           .Include(x => x.PublishedByUser)
                                           .Include(x => x.ModifiedByUser)
                                           .Include(x => x.Tags)
                                           .ThenInclude(x => x.Topic)
                                           .Include(x => x.AdminTags)
                                           .ThenInclude(x => x.AdminTag)
                                           .Where(x => !x.IsDeleted && !x.IsHidden)
                         on tag.VideoId equals videoItem.Id
                         where tag.VideoId != id && !videoItem.IsDeleted
                         select videoItem).Take(2).ToList();

           var relatedExperiences = new List<RelatedExpirienceResponse>();
           for ( int i = 0; i < items.Count; i++ )
           {
               var item = _mapper.Map<RelatedExpirienceResponse>(items[i]);
               item.IsLiked = items[i].Like.Any(x => x.UserId == userId);
               relatedExperiences.Add(item);
           }
           response.RealtedExpiriences.AddRange(relatedExperiences);

           return response;
       }

Answer 1

(Cross-posted from CodeProject )

I suspect it's because you're trying to join an in-memory list to a database table.

Try:

var topicIds = video.Tags.Select(x => x.TopicId).ToList();
var items = (from tag in _context.VideoTagLink.Where(t => topicIds.Contains(t.TopicId))
             join videoItem in _context.Videos
                 .Include(x => x.CreatedByUser)
                 .Include(x => x.Like)
                 .Include(x => x.PublishedByUser)
                 .Include(x => x.ModifiedByUser)
                 .Include(x => x.Tags)
                 .ThenInclude(x => x.Topic)
                 .Include(x => x.AdminTags)
                 .ThenInclude(x => x.AdminTag)
                 .Where(x => !x.IsDeleted && !x.IsHidden)
             on tag.VideoId equals videoItem.Id
             where tag.VideoId != id && !videoItem.IsDeleted
             select videoItem).Take(2).ToList();