How to apply query boost on certain fields

Question

I am using regular ContentSearch API in front of Coveo for Sitecore 3 (not using Coveo UI). I am trying to boost keywords in Title and Subtitle fields to have higher weights compared to page Content. Unfortunately my current approach does not seem to work. Ideally I would like to see results that has keywords match in Title field to show up on top of search results.

Is there another way to weigh certain fields over others in Coveo and ContentSearch?

private Expression<Func<T, bool>> GetPredicate<T>(string criteria, string location, string language) where T : SearchResultItem
    {
        var predicate = PredicateBuilder.True<T>();
        predicate = predicate.And(
            x => x.Language == language);

        predicate = predicate.And(
            x => x.Path.Contains(location));

        predicate = predicate.And(
            x => x.TemplateId == TemplateIds.ArticlePageTemplateId
              || x.TemplateId == TemplateIds.GroupPageTemplateId);

        var termPredicate = PredicateBuilder.True<T>();
        foreach (var term in criteria.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries))
        {
            termPredicate = termPredicate.And(p => p.Content.Contains(term)
            || p["Title"].Contains(term).Boost(3f)
            || p["Subtitle"].Contains(term).Boost(2f));
        }
        predicate = predicate.And(termPredicate);

        return predicate;
    }

Answer 1

Coveo should support .Boost() like Lucene as mentioned in the supported LINQ operators.

I do not know if this applies to your use case, but it is worth noting that Coveo for Sitecore ships with a specific CoveoBoost extension that supports boosting results according to fields like so:

queryable.CoveoBoost(item => item.Field == "value" || item.Field2 == "value2", 200)

Note that your number should be high enough, we consider around 100 to be a "great boost", so you should probably try with higher numbers too.

Answer 2

Sitecore's LINQ .Contains method translates to a WildcardQuery, which can't be boosted in native Lucene.

You can check the Lucene.Net question here: https://stackoverflow.com/questions/10352404/lucene-net-boost-not-working-when-using-wildcard

As Sitecore depends on the Lucene.Net, wildcard queries boosting won't work here.

However, boosing still works on exact matches, like Equals, etc.