regex - Caseless matching using views in Cloudant -

i have database of documents have following data structure:

{     "_id": "sampleid",     "_rev": "sample-rev",     "added": "2014-09-09 01:05:32",     "cached": 1,     "subject": "sample topic",     "mode": "<samplemode>",     "protected": 0,     "added_by": "myname",     "factoid": "sample factoid" } 

and have following view:

function(doc) {     if (doc.subject && doc.factoid && doc.mode){         emit(doc.subject, doc.factoid);     } } 

i need retrieve docs "subject" matches provided key. non case sensitive. post give me of matches want, if case matches.

https://<username>.cloudant.com/<db>/_design/<designdoc>/_view/<view>?include_docs=true  { "keys" : ["<subject>"] } 

i have tried search indexes without success. api mentions regex operator haven't been able working. seems simple thing, how should approaching this?

regarding $regex approach, here i'm at. following post works previous attempts @ returning case-sensitive results.

https://<username>.cloudant.com/<db>/_find  {     "selector": {         "subject": {"$eq": "<subject>"}     },     "fields": ["_id", "_rev", "subject", "factoid"] } 

substituting $regex operator $eq yields following error:

{ "error": "no_usable_index", "reason": "there no operator in selector can used index." } 

the reference material function rather slim. mentioned on page: https://docs.cloudant.com/api/cloudant-query.html

one option create secondary index stores uppercased search string:

function(doc) {     if (doc.subject){         emit(doc.subject.touppercase());     } } 

the application can uppercase search criteria before sending database:

https://username.cloudant.com/database/_design/designdoc/_view/view?key=“sample topic"&include_docs=true 

will result in this:

{     "offset": 0,     "rows": [         {             "doc": {                 "_id": "sampleid",                 "_rev": "1-d77a468b74497771f8d37130a7cf02eb",                 "added": "2014-09-09 01:05:32",                 "added_by": "myname",                 "cached": 1,                 "factoid": "sample factoid",                 "mode": "<samplemode>",                 "protected": 0,                 "subject": "sample topic"             },             "id": "sampleid",             "key": "sample topic",             "value": null         }     ],     "total_rows": 1 }