TypeSearchExtensions.cs

public static IQueriedSearch<T> AddMatchingQueryStringFor<T>(this ITypeSearch<T> search, string queryString, Expression<Func<T, string>> fieldSelector)
{
    var fieldName = search.Client.Conventions.FieldNameConvention
        .GetFieldNameForAnalyzed(fieldSelector);

    //Split words by space
    string[] words = queryString.Split(' ');

    return new Search<T, WildcardQuery>(search, context =>
    {
        var boolQuery = new BoolQuery();

        //Make sure to add existing query to our bool query as a required condition
        if (context.RequestBody.Query != null)
            boolQuery.Must.Add(context.RequestBody.Query);

        foreach (string word in words)
        {
            //Add a wild card query for each word. Stars represents that is matches the single word
            var wildcardQuery = new WildcardQuery(fieldName, String.Format("*{0}*", word.ToLowerInvariant()));
            boolQuery.Should.Add(wildcardQuery);
        }

        //Require none off our should match points, as these are optional but may mean that a result is included
        boolQuery.MinimumNumberShouldMatch = 0;

        context.RequestBody.Query = boolQuery;
    });
}