populating associations in mongodb -

i'm new mean , mongodb , trying figure out how populate answers questions. changed words in platform i'm learning (examples posts , comments).

here's error message i'm getting.

/users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/express/lib/view.js:62 throw new error('no default engine specified , no extension prov       ^ error: no default engine specified , no extension provided. @ new view (/users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/express/lib/view.js:62:11) @ eventemitter.render (/users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/express/lib/application.js:569:12) @ serverresponse.render (/users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/express/lib/response.js:961:7) @ /users/joerigby/documents/codingdojo/full mean/blacktest3/server/controllers/answers_c.js:53:12 @ query.<anonymous> (/users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/mongoose/lib/query.js:2112:28) @ /users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/mongoose/node_modules/kareem/index.js:177:19 @ /users/joerigby/documents/codingdojo/full mean/blacktest3/node_modules/mongoose/node_modules/kareem/index.js:109:16 @ process._tickcallback (node.js:355:11) 24 aug 16:48:22 - [nodemon] app crashed - waiting file changes before starting... 

below codes..

from answers_controller.js on server side

    show: function(req, res){         console.log(req.params.id);          question.findone({_id: req.params.id})                 .populate('answers')           .exec(function(err, question) {             res.render('question', {question: question});                 });             }     } 

from answer model

var mongoose = require('mongoose'); var schema = mongoose.schema; var objectid = require('mongodb').objectid;  var answerschema = new mongoose.schema({     answer: string,     description: string,     likes: {type: number, default: 0},     created_at: {type: date, default: date.now },     _question: {type: schema.objectid, ref: 'question'} }); mongoose.model('answer', answerschema); 

from question model

var mongoose = require('mongoose'); var schema = mongoose.schema;  var objectid = require('mongodb').objectid;   var questionschema = new mongoose.schema({   title: string,   description: string,   created_at: {type: date, default: date.now },   answers: [{type: schema.types.objectid, ref: 'answer'}] }); mongoose.model('question', questionschema); 

let me know if need else at. time.

the error not mongo or mongoose. check stack trace in error message. problem res.render. in order use method must either configure express have default view engine (ejs, jade, etc.) or provide file extension after 'question' knows template file in order render html.

// in main server file  // set default view engine app.set('view engine', 'ejs'); // set view folder (where looks template files app.set('views', pathtoviewfolder); 

now can create question.ejs file in folder @ pathtoviewfolder.