group in mongo excluding null values

Question

I have mongo query which does the group operation on the documents.

I have almost got the expected results except that I want to refine the results without empty or null values.

Currently my query looks like this:

db.productMetadata.aggregate([{$group:{"_id":{"color":"$productAttribute.colour","gender":"$productAttribute.gender"},"count" : {$sum : 1}}}]); 

And the results looks something like this:

{ "_id" : { "color" : "BLUE", "gender" : "MEN" }, "count" : 1 } { "_id" : {  }, "count" : 4 } { "_id" : { "color" : "NA", "gender" : "WOMEN" }, "count" : 1 } { "_id" : { "color" : "BLACK", "gender" : "MEN" }, "count" : 1 } { "_id" : { "color" : "BROWN", "gender" : "WOMEN" }, "count" : 1 } { "_id" : { "gender" : "MEN" }, "count" : 2 } { "_id" : { "color" : "BEIGE", "gender" : "MEN" }, "count" : 1 } { "_id" : { "color" : "BROWN", "gender" : "MEN" }, "count" : 1 } 

I want to remove the rows if any of the group by field values are empty or null in the actual data of DB.

Excepted results should look something like this:

{ "_id" : { "color" : "BLUE", "gender" : "MEN" }, "count" : 1 } { "_id" : { "color" : "NA", "gender" : "WOMEN" }, "count" : 1 } { "_id" : { "color" : "BLACK", "gender" : "MEN" }, "count" : 1 } { "_id" : { "color" : "BROWN", "gender" : "WOMEN" }, "count" : 1 } { "_id" : { "color" : "BEIGE", "gender" : "MEN" }, "count" : 1 } { "_id" : { "color" : "BROWN", "gender" : "MEN" }, "count" : 1 } 

Answer 1

You need an extra $match pipeline step that will filter the incoming documents based on the embedded field "$productAttribute.colour" existing and not null:

    db.productMetadata.aggregate([     {          "$match": {             "productAttribute.colour": {                  "$exists": true,                  "$ne": null              }         }         },     {          "$group": {             "_id": {                 "color": "$productAttribute.colour",                 "gender": "$productAttribute.gender"             },             "count": {                  "$sum": 1              }         }        }         ]);