mongodb - Moongoose aggregate $match does not match id's -


i want show products ids (56e641d4864e5b780bb992c6 , 56e65504a323ee0812e511f2) , show price after subtracted discount if available.

i can count final price using aggregate, return document in collection, how make return matches ids

"_id" : objectid("56e641d4864e5b780bb992c6"),  "title" : "keyboard",  "discount" : numberint(10), "price" : numberint(1000)  "_id" : objectid("56e65504a323ee0812e511f2"),  "title" : "mouse",  "discount" : numberint(0), "price" : numberint(1000)  "_id" : objectid("56d90714a48d2eb40cc601a5"),  "title" : "speaker",  "discount" : numberint(10), "price" : numberint(1000)

this query

productmodel.aggregate([         {             $project: {                 title   : 1,                 price: {                     $cond: {                         if: {$gt: ["$discount", 0]}, then: {$subtract: ["$price", {$divide: [{$multiply: ["$price", "$discount"]}, 100]}]}, else: "$price"                     }                  }             }         }     ], function(err, docs){         if (err){             console.log(err)         }else{             console.log(docs)         }     })

and if add $in query, returns empty array 

productmodel.aggregate([             {                 $match: {_id: {$in: ids}}             },             {                 $project: {                     title   : 1,                     price: {                         $cond: {                             if: {$gt: ["$discount", 0]}, then: {$subtract: ["$price", {$divide: [{$multiply: ["$price", "$discount"]}, 100]}]}, else: "$price"                     }                  }             }         }     ], function(err, docs){         if (err){             console.log(err)         }else{             console.log(docs)         }     })

your ids variable constructed of "strings", , not objectid values.

mongoose "autocasts" string values objectid correct type in regular queries, does not happen in aggregation pipeline, in described in issue #1399.

instead must correct casting type manually:

ids = ids.map(function(el) { return mongoose.types.objectid(el) })

then can use them in pipeline stage:

{ "$match": { "_id": { "$in": ids } } }

the reason because aggregation pipelines "typically" alter document structure, , therefore mongoose makes no presumption "schema" applies document in given pipeline stage.

it arguable "first" pipeline stage when $match stage should this, since indeed document not altered. right not how happens.

any values may possibly "strings" or @ least not correct bson type need manually cast in order match.


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