How to query for regEx matches in any value in a stringCollection field?

Question

I have a computed field with returnType="stringCollection", which I am using via a search result model that looks something like this:

public class MySearchResultItem : SearchResultItem
{
    // ...other properties...

    [IndexField("aliases")]
    public string[] Aliases {get; set;}
}

My search code needs to find results that have aliases beginning with a given letter (or any digit if the input is #). Here's what it looks like now:

var pattern = (letter == "#" ? "[0-9]" : letter) + ".*";
var predicate = PredicateBuilder.True<MySearchResultItem>();
// ...other clauses...
predicate = predicate.And(r => r.Aliases.Any(a => a.Matches(pattern));
var results = context.GetQueryable<MySearchResult>().Where(predicate).ToList();

Originally, I had the Aliases property as an IEnumberable<string>, but I got an error that said it must be an array. After changing it to an array, I get an exception like so:

[ArgumentException: Static method requires null instance, non-static method requires non-null instance.
Parameter name: instance]
   System.Linq.Expressions.Expression.ValidateStaticOrInstanceMethod(Expression instance, MethodInfo method) +5862475
   System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, IEnumerable`1 arguments) +69
   Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.VisitLinqEnumerableAnyMethod(MethodCallExpression methodCall) +573
   Sitecore.ContentSearch.Linq.Parsing.ExpressionParser.Visit(Expression expression) +186
   ...
   System.Linq.Enumerable.ToList(IEnumerable`1 source) +70
   ... my code ...

Am I doing something wrong, or is this kind of query just not supported by the API?

If this isn't supported, is there another way to get there? Changing it from Matches to StartsWith(letter) gets rid of the error, but I would need to add 10 StartsWith clauses for the digit case and apparently StartsWith isn't "safe" to begin with.

Answer 1

When working with stringCollection fields, you can declare them in the model simply as string. When you apply any filtering logic to such a field, that logic will be treated as .Any(), meaning that the filter needs to apply to at least one string in the collection. This is in a way similar to how tokenized fields work.

Define your field in the model like this:

[IndexField("aliases")]
public string Aliases { get; set; }

And then filter like this:

predicate = predicate.And(r => r.Aliases.Matches(pattern));