Sitecore Solr Search by Multilist with Values from Another Multilist

I have a set of product items. Each product item has a multilist field that points to a set of product type items. When on a product page, I want to show a paged list of related items. These should be items that share a product type with the currently selected item. I'm running into some trouble because products can have multiple types. I need to split the type list on the current item and check that against the list of products in an expression. For some reason split and contains are throwing runtime exceptions and I can't really figure out why. I saw some things about the predicate builder being used for dynamic queries and I will try to use that with what I currently have but I'd like to know why this can't be done straight in the where clause.

Another issue I ran into is that the list of ids stored in solr are being stripped of their '{', '}', and '-' characters.

If you are already on the product page I assume you already have the product item and that product item should have a "ProductType" multilist field. You can use Sitecore.Data.Fields.MultilistFiled to avoid worrying about have to split the raw values.

You can then use Sitecore's Predicate Builder to build out your search predicate, which I assume you want to find all products that have one similar product type. You should adjust this search logic as needed. I am using the ObjectIndexerKey (see more here -> http://www.sitecore.net/Learn/Blogs/Technical-Blogs/Sitecore-7-Development-Team/Posts/2013/05/Sitecore-7-Predicate-Builder.aspx) to go after a named field, but you should build out a proper search model and actually define ProductTypes as a List< ID> or something similar. You may need to add other conditions to the search predicate as well such as path or templateid to limit your results. After that you can just execute the search and consume the results.

As far as Solr stripping the special characters, this is expected behavior based on the Analyzer used on the field. Sitecore and Solr will apply the proper query time analyzers to match things up so you shouldn't have to worry about formatting as long as the proper types are used.

var pred = PredicateBuilder.True<SearchResultItem>();

Sitecore.Data.Fields.MultilistField multilistField = Sitecore.Context.Item.Fields["ProductTypes"];
if (multilistField != null)
{
     foreach (ID id in multilistField.TargetIDs)
     {
          pred = pred.Or(x => ((ID)x[(ObjectIndexerKey)"ProductType"]).Contains(id);
     }
}


ISearchIndex _searchIndex = ContentSearchManager.GetIndex("sitecore_master_index");  // change to proper search index

using (var context = _searchIndex.CreateSearchContext())
{
     var relatedProducts = context.GetQueryable<SearchResultItemModel>().Where(pred);

     foreach(var relatedProduct in relatedProducts)
     {
          // do something here with search results
     }
}