Tridion Publisher and Custom Resolvers

Back in the day, we used to disable Tridion's link resolving (aka "Link Propagation") at publish time by using the old and venerable Event System (for more details about link resolving, check this page).

Recently I had to write some code to disable link resolving only under certain conditions for Tridion 2009, and started going down the true-and-tried road of Event System and "OnComponentPublishPre" events. Shortly after deployment in the test environment we started getting some really angry error messages from COM saying that my code was trying invalid casts.

Obviously offended by the suggestion that my code wouldn't work, I tried to understand what the **** was going on, and eventually figured out that it was all down to this: MSXML cannot be used in .NET code. And since the Event System in pre-2011 days is still based on COM and the Publish Instruction is an MSXML document... it would never work.

I could have re-written my Event System in VB6... but let's not even go down that path.

After scratching my head for about half a second, and some nudging from @puf on the right direction, I decided to try writing a Custom Resolver for the Tridion Publisher.

And I was so amazed with the results that I thought I should share it with you.

There's quite a few differences between a Custom Resolver and the Event System approach, the main ones being that you write your code in native .NET (using TOM.NET objects) and that you do not completely disable link resolving - you just fiddle with the results instead.

Another great advantage of a Custom Resolver is that it is forwards-compatible: the code you write for Tridion 5.3 or 2009 will also work with Tridion 2011(*).

So, let's get to the code, shall we?

Create a class library, add references to Tridion.Common, Tridion.ContentManager and Tridion.ContentManager.Publishing.

Create a class that implements the Tridion.ContentManager.Publishing.Resolving.IResolver interface.

Create a void method as follows:

public void Resolve(IdentifiableObject item, ResolveInstruction instruction, PublishContext context, Tridion.Collections.ISet <ResolvedItem> resolvedItems)

The resolvedItems collection is exactly what it looks like: this is the list of items that will be published unless we interfere with it. It's just a collection, so feel free to iterate through it, determine its type, remove items from it, etc. There's a reasonably good sample on the Tridion docs, just search for Custom Resolver.

Just a few more words on the deployment:

• The assembly you create must go into the GAC
• You have to add your assembly to the Tridion.ContentManager.Config file in the "resolvers" section AFTER the default resolver from Tridion
• Restart the publisher and you're in business

(*) Hotfix CM_2011.0.1.74870 required in this pre-Service Pack 1 world.