Testing for empty arrays in Mongodb

Question

I'm looking for documents that have both 'e-campaigns' and 'p-campaigns' arrays that are non-empty:

 db.coll.find( { 'p-campaigns':{$ne:[]} ,  'e-campaigns' : {$ne:[]} }     )

I run the query on each array separately and do find docs with non-empty p-campaigns and e-campaigns, but the combined conditions turns out empty. I know there are documents with both p-campaigns and e-campaigns non-empty. I've tried using $and, with the same result: no docs with both arrays non-empty.

Am I going about this the right way? If not, why? This seems like the logical way to run this query on the conditions above. Thanks.

You can test for position 0, i.e.: 'e-campaigns.0':{$exists:true} — Sammaye
– Sammaye, Commented Sep 2, 2013 at 13:14

Artem Mezhenin · Accepted Answer · 2013-09-02 13:17:26Z

1

Here is my variant:

> db.a.save({x:[], y:[]})
> db.a.save({x:[1], y:[]})
> db.a.save({x:[], y:[1]})
> db.a.save({x:[1], y:[1]})
> db.a.find()
{ "_id" : ObjectId("52248f5efb41276d1f3e3164"), "x" : [ ], "y" : [ ] }
{ "_id" : ObjectId("52248f61fb41276d1f3e3165"), "x" : [ 1 ], "y" : [ ] }
{ "_id" : ObjectId("52248f66fb41276d1f3e3166"), "x" : [ ], "y" : [ 1 ] }
{ "_id" : ObjectId("52248f69fb41276d1f3e3167"), "x" : [ 1 ], "y" : [ 1 ] }
> db.a.find({ 'x':{$ne:[]} ,  'y' : {$ne:[]} })
{ "_id" : ObjectId("52248f69fb41276d1f3e3167"), "x" : [ 1 ], "y" : [ 1 ] }

answered Sep 2, 2013 at 13:17

Artem Mezhenin

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2 Comments

user2105469 Over a year ago

It's comforting to see I do understand the querying, but clearly I'm clobbering records with my updates. Back to the manual... Thanks.

Asya Kamsky Over a year ago

this won't work if the field doesn't exist at all - it only works if it's guaranteed to be exactly an empty array.

Praveen Kumar Verma · Accepted Answer · 2023-08-21 13:27:47Z

0

For empty array in mongoDb filter query:

{field: {$size: 0}} // When find field array size is 0 or empty.

answered Aug 21, 2023 at 13:27

Praveen Kumar Verma

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