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 }