mongodb - Locating a specific record in an aggregation of a Mongo DB collection -


i working on reporting project deal monthly orders have orders coming mongodb in below format

order:{  _id: 123456789012123456789012,  items:[     {code:'item1', qty:5},{code:'item2', qty:6}  ] }

my requirement find out how specific item ranks against other items in on performance

i wrote aggregation first find out grouping of each item , number of quantities ordered

db.orders.aggregate(   [     { $unwind : "$items" },     { $group : {code : "$code" , tot_ord: { $sum : "$qty" } } },     { $sort : { tot_ord : -1 } }   ] )

so should give me sorted list of items highest orders first.

but how rank of specific item without looping? talking 500,000 different items want avoid looping

thanks in advance.

update: had working. example using node.js. posting useful in future

function aggregate(mongodb,collection_item, pipeline, next){         mongodb.collection(collection_item, function(err, collection) {         collection.aggregate(pipeline,function(err,result) {                         if(err){                 console.log('error aggregating: ' + err);                 next({'error':'an error has occurred - ' + err});             }else{                 next(result);                 }                     });             }); }  function calculateorderrank(itemid){      aggregate(mongodb, "orders",              [               { $unwind : "$items" },               { $match : { items.code : itemid} },                             { $group : { _id : "$items.code" , tot_qty: { $sum : "$items.qty" } } }              ],function(result) {                 var itemqty = result[0].tot_qty;                 data.aggregate(mongodb, "orders",                  [                   { $unwind : "$items" },                   { $group : { _id : "$items.code" , tot_qty: { $sum : "$items.qty" } } },                   { $match: {tot_qty:{$gt:itemqty}} },                   { $group : {_id:null, rank : { $sum : 1 } } },                 ],function(result) {                     var rank = 1;                     if (result && result.length>0) {                         rank = result[0].rank + 1;                     }                     res.send({item_id:itemid, rank:rank, score:itemqty});                 });             }     );  }

this feature not exist in aggregation framework @ time. need jira.mongodb.org/browse/server-8065 implemented able rankings.

meanwhile can 2 aggregation framework queries.

the first 1 aggregate , totals specific item in question (it similar include in question, $group format incorrect, should {$group: {_id:"$items.code", <etc>}). start limiting "items.code" particular value.

the second 1 collection , after aggregation {match:{count:{$gt:<count-for-that-one-item>}} , $group count how many "totals" higher 1 item's. gives item's rank.


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