Episerver Find - Conditional Sorting?

A client asked me if it was possible to push a specific variation to the top of a list that is coming from Find. I immediately replied "Of course!", since like most things working with development, almost everything is possible; It's just a matter of time/effort, and I thought it would be a quick change.

When I first looked into the task, I noticed that the list was set to order by the variations SortOrder and not score, so boosting wasn't really an option.

SearchClient.Instance.Search<VariationContent>()
	.Filter(x => x.Parents.Match(refId.ToString()))
	…… // Other visibility conditions, facets/terms/skip/take etc
	.OrderBy(x => x.SortOrder)
	.GetResult();

My next step was to see if there are any possibilities do to a conditional sort, as in sorting with filters, or perhaps using custom script sorting which you can do with Elasticsearch that Episerver Find is based upon. After a lot of googling and plowing through a lot of interesting blog posts and questions on world.episerver.com, I couldn't find anything that was related to my task.

Next step was to do some reflection of the Episerver.Find assembly. What I found there was that it IS possible, IF you were sorting by nested objects, using the following method in the Episerver.Find.NestedSortingExtensions class

.OrderBy(enumerableFieldSelector, itemFieldSelector, filterExpression)

Unfortunately, there aren't any existing methods that does what I was looking for, e.g.

.OrderBy(fieldSelector, filterExpression)

Taking another look at the Find SDK, I stumbled upon .Include(filterExpression, boostMultiplier), which, together with the extension .ThenByScore(), written by Henrik Lindström, that we already use, would help me with my task.

.Include(filterExpression, boostMultiplier) allowes me to:

1. Search for my specific item, using the regular .For(query) with the .InField(fieldSelector) and .Filter(filterExpression)
2. Get the rest of the variations with the same boosting score (since they don't get a hit in the .For), that I can then order using the field SortOrder, just like before.

The final solution was

SearchClient.Instance.Search<VariationContent>()
	.For(itemId)
	.InField(x => x.ItemId)
	.Filter(x => x.Parents.Match(refId.ToString()))
	.Include(x => x.Parents.Match(refId.ToString()), 1)
	…… // Other visibility conditions, facets/terms/skip/take etc
	.OrderByScore()
	.ThenBy(x => x.SortOrder)
	.GetResult();

I'm sure there are multiple ways to achieve the same results, but this was the simplest way I could do it and it might help someone else.

Cheers! /
Stellan Danald,
Solutions Architect @ Nansen