Dynamically filter on number using LINQ

Question

I have numeric fields that I want to filter on with a range, however, these need to be dynamic using the SearchResultItem's property indexer. The code I'm currently using is:

var predicate = PredicateBuilder.False<SearchResultItem>();

return predicate.Or(i => (double)i[(ObjectIndexerKey)"price"] > 20 && (double)i[(ObjectIndexerKey)"price"] <= 40);

However, this doesn't appear to be working. In the search log, I can see that the query being produced is:

+(+price:{20 TO *] +price:[* TO 39.99])

The first thing is that this looks like a syntax bug to me? There is a curly brace instead of a square bracket. Unsurprisingly Luke will not parse this:

Cannot parse '+(+price:{20 TO *] +price:[* TO 39.99])': Encountered " <RANGEEX_GOOP> "+price:[* "" at line 1, column 19. Was expecting: "}" ...

If I change the expression in Luke to:

+price:[20 TO 50]

Then it works and I get back the expected documents. How can I write the Linq to achieve the same?

UPDATE:

Figured out the syntax:

return predicate.Or(i => ((double)i[(ObjectIndexerKey)"price"]).Between(20, 40, Inclusion.Both));

Using the extension method:

Sitecore.ContentSearch.Linq.Between

This produces the following in the search log:

12136 10:14:23 INFO  ExecuteQueryAgainstLucene (sitecore_master_index): +price:[20 TO 40] - Filter : 

If I put

+price:[20 TO 40] 

Into Luke, it returns the documents I expect to see. Yet in code, no results come back?

UPDATE 2

I think I've tracked this down to this flag (which is incidentally connected to my problems on this question):

The legend for this flag in Luke describes it as "Indexed". This currently not set and the sort & filtering doesn't work when this is not set. I had previously got the sort working and noticed that this was set. Since rebuilding the index, it's no longer set. But I haven't changed anything so I don't know what is controlling that flag?

Answer 1

Figured it out:

return predicate.Or(i => ((double)i[(ObjectIndexerKey)"price"]).Between(20, 40, Inclusion.Both));

Using the extension method:

Sitecore.ContentSearch.Linq.Between

The other thing I needed to do was ensure that the field is configured as TOKENIZED:

      <field fieldName="price"
         storageType="YES"
         indexType="TOKENIZED"
         vectorType="NO"
         boost="1f"
         type="System.Double" settingType="Sitecore.ContentSearch.LuceneProvider.LuceneSearchFieldConfiguration, Sitecore.ContentSearch.LuceneProvider" />

This seems to ensure that flag is set in Luke which seems to determine whether sorting & filtering works on the field.