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Count by multiple fields with MongoDB aggregation
To count by multiple fields, use $facet in MongoDB. The $facet processes multiple aggregation pipelines within a single stage on the same set of input documents. Let us create a collection with documents −
> db.demo721.insertOne( ... { ... ... "details1": { ... "id":101 ... ... }, ... "details2": { ... "id":101 ... }, ... "details3": { ... "id":101 ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5eaaebdd43417811278f5887") } > > > db.demo721.insertOne( ... { ... ... "details1": { ... "id":101 ... ... }, ... "details2": { ... "id":102 ... }, ... "details3": { ... "id":102 ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5eaaebe943417811278f5888") }
Display all documents from a collection with the help of find() method −
> db.demo721.find();
This will produce the following output −
{ "_id" : ObjectId("5eaaebdd43417811278f5887"), "details1" : { "id" : 101 }, "details2" : { "id" : 101 }, "details3" : { "id" : 101 } } { "_id" : ObjectId("5eaaebe943417811278f5888"), "details1" : { "id" : 101 }, "details2" : { "id" : 102 }, "details3" : { "id" : 102 } }
Following is the query to count by multiple fields −
> db.demo721.aggregate([ ... {$facet:{ ... ids:[ ... {$group:{ _id:null, ... d3:{$addToSet: "$details3.id"}, ... d2:{$addToSet:"$details2.id"}, ... d1:{$addToSet:"$details1.id"}}}, ... {$project:{ _id:0, ... listofall:{$setUnion:["$d1","$d2","$d3"]}}}], ... d:[{$project:{ _id:0, ... a1:"$details1.id", ... a2:"$details2.id", ... a3:"$details3.id"}}]}}, ... {$unwind:"$d"}, ... {$unwind:"$ids"}, ... {$unwind:"$ids.listofall"}, ... {$group:{ _id:"$ids.listofall", ... details1id:{$sum:{$cond:[{$eq:["$d.a1","$ids.listofall"]},1,0]}}, ... details2id:{$sum:{$cond:[{$eq:["$d.a2","$ids.listofall"]},1,0]}}, ... details3id:{$sum:{$cond:[{$eq:["$d.a3","$ids.listofall"]},1,0]}}}}])
This will produce the following output −
{ "_id" : 102, "details1id" : 0, "details2id" : 1, "details3id" : 1 } { "_id" : 101, "details1id" : 2, "details2id" : 1, "details3id" : 1 }
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