java - Spring Data MongoDB: aggregation framework - sort with nested property throws invalid reference -

i found this article in spring forum dicusses partly same problem, has no answer question.

given following document...

{     "_id": { "$oid": "5214b5d529ee12460939e2ba"},     "title": "this title",     "tags": [ "fun", "sport" ],     "comments": [         {             "author": "alex",             "text": "this cool",             "createdat": 1         },         {             "author": "sam",             "text": "this bad",             "createdat": 2         },         {             "author": "jenny",             "text": "this bad",             "createdat": 3         }     ] } 

... want aggregation (javascript) ...

//this concise possible focus on actual problem sort operation when ported spring!   db.articles.aggregate(      {$unwind:"$comments"},     //do more match, group, etc...     {$sort:{"comments.createdat":-1}} //sort descending -> here problem occurs in spring (works in javascript!) ); 

... spring -> throws invalid reference!

aggregation agg = newaggregation(        unwind("comments"),        sort(direction.desc, "comments.createdat") //throws invalid reference 'comments.createdat'!        //how can make work?  ); 

of course can native java-driver , without usage of spring's mongotemplate don't approach much. can make exact aggregation work spring?

i using current version 1.4.0.release.

the code posted indeed works - problem had else.

i did this:

aggregation agg = newaggregation(        project("comments"), //this problem! without works desired!        unwind("comments"),        sort(direction.desc, "comments.createdat")  ); 

as wrote in code wanted project comments-field save overhead - acutally caused problem!

thanks lot hint!