node.js/mongoDB: Return custom value if field is null -

node.js/mongoDB: Return custom value if field is null -

what want query database documents and, if field not set, homecoming custom value instead of it.

imagine i'm having collection of songs , of these have field pathtocover set , don't. these, want homecoming url placeholder image store in config variable.

i running node.js , mongodb express , mongoose.

i not sure best approach is. obvious solution query documents , in callback iterate on them check if field set. feels quite superfluous.

currently, code looks this:

exports.getbyalbum = function listbyalbum(query, callback) { song.aggregate({ $group: { _id: '$album', artists: { $addtoset: '$artist' }, songs: { $push: '$title' }, covers: { $addtoset: '$pathtocover'}, genres: { $addtoset: '$genre'}, pathtocover: { $first: '$pathtocover'} } }, function (err, result) { if (err) homecoming handleerror(err); result.foreach(function(album) { if ( album.pathtocover == null) { album.pathtocover = config.library.placeholders.get('album'); } }) callback(result); }); }

what best approach this?

thanks lot in advance!

where value of field either null or unset , perchance missing document, utilize $ifnull in aggregation set alternate value:

exports.getbyalbum = function listbyalbum(query, callback) { var defaultcover = config.library.placeholders.get('album'); song.aggregate( [ { "$group": { "_id": "$album", "artists": { "$addtoset": "$artist" }, "songs": { "$push": "$title" }, "covers": { "$addtoset": { "$ifnull": [ "$pathtocover", defaultcover ] } }, "genres": { "$addtoset": "$genre" }, "pathtocover": { "$first": { "$ifnull": [ "$pathtocover", defaultcover ] } } }} ], function (err, result) { if (err) homecoming handleerror(err); callback(result); } ); }

if empty string utilize $cond statement $eq test in place of $ifnull:

{ "$cond": [ { "$eq": [ "$pathtocover", "" ] }, defaultcover, "$pathtocover" ] }

either statement can used within of grouping operator replace value considered.

if worried perhaps not "all" of values set on song, utilize $min or $max appropriate info pick 1 of values instead of using $first.

node.js mongodb mongoose mongodb-query aggregation-framework