Hi all,

We are planning a caching strategy for our project.
Caching whole pages is not an options for us.
We are thinking of caching blocks.

Currently, we are trying to use

[OutputCache(VaryByParam = "currentBlock", VaryByCustom = "language", Duration = 60 * 15)]

with ToString on block overriden like this:

 public override string ToString()
        {
            IContent content = this as IContent;
            IChangeTrackable changetrackable = this as IChangeTrackable;

            var test = EPiServer.ServiceLocation.ServiceLocator.Current.GetInstance();

            if (content != null && changetrackable != null)
            {
                return $"{content.ContentLink}-{changetrackable.Saved.Ticks}-{EPiServer.Editor.PageEditing.PageIsInEditMode}";
            }

            return base.ToString();
        }

and in Global.asax:

 public override string GetVaryByCustomString(HttpContext context, string custom)
        {
            if (custom == "language")
            {
                return ContentLanguage.PreferredCulture.Name;
            }
            return base.GetVaryByCustomString(context, custom);
        }

However, this solution doesn't support the following cases:

1. blocks in blocks - in case inner block is changed, cache for parent block is not flushed
2. blocks in RTE property of page/block - same issue as in 1.
3. Personalized content inside block.

For 1. I have an idea of getting parent blocks and republish them on inner block publish like this:

if (e.Content is IInnerBlockMarker)
            {
                var repository = ServiceLocator.Current.GetInstance();
                var parentBlocks = repository.GetReferencesToContent(e.ContentLink, false).
                    Select(r => r.OwnerID).Select(id => repository.Get(id)).ToArray();
                var filter = new FilterPublished();
                filter.Filter(parentBlocks);
                var blocks = parentBlocks.Select(s => s as CacheableBlock).Where(s => s != null).Distinct().ToArray();
                Array.ForEach(blocks, (b) =>
                {

                    var bToUpdate = b.CreateWritableClone() as IContent;

                    (bToUpdate as IChangeTrackable).Saved = DateTime.Now;
                    repository.Save(bToUpdate, EPiServer.DataAccess.SaveAction.Publish, EPiServer.Security.AccessLevel.Publish);
                }

For 3. I found the solution in the Internet which basically is an extenstion of custom string:

if (custom == "visitorGroupHash")
            {
                var helper = new VisitorGroupHelper();
                StringBuilder sb = new StringBuilder();
                foreach (var role in GetRolesForContext(context))
                {
                    sb.Append(role);
                    sb.Append(helper.IsPrincipalInGroup(context.User, role));
                    sb.Append("|");
                }
                return sb.ToString();
            }

My wish is to not do more harm than good. My solution for 1. may take a long time on publish if inner block has a lot of parents and I have to also take into account whether the parent block has scheduled publishing or not. And what about block inside a block inside a block? My solution doesn't support that.

My solution for 3. may clutter the memory with multiple versions for each block.

Do you know better output cache strategy?

Thank you in advance for your help.