I have a document in Mongo that is structured in the following way:
{
"_id" : ObjectId("4eea7237d0ba3a04f20008fb"),
"code" : "b2677c2809c844cc9d7e3e4ff8d95b46",
"city_id" : 4,
"datetime" : ISODate("2011-12-13T18:41:44.062Z"),
"plays" : [
{
"play_id" : 717224,
"clicks" : [ ],
"order" : 1,
"mysql_id" : 145
}
I want to query for docs whose plays.clicks attribute is a non-empty list. I've tried exists with no luck. I thought that something like this might work:
db.collection.find({plays.clicks.0: {$exists:true}})
But I believe that this would return only docs whose first element in the plays array contains a non-empty clicks list.
Any thought on how I might get this done?
Thanks
db.collection.find({plays.clicks.0: {$exists:true}})
is the right syntax, however as plays
is a list the query will match any document that has clicks in plays
. There is no way to retrieve a subset of an Array for subelements in this way[1]. There is a ticket for sub / virtual collections[2]
Save the size of the list as a separate attribute (eg num_plays
). Then you can query for documents where num_plays
is greater than 0
:
Haven't tested, but I think the query you want is
{ "plays.clicks" : { "$size" : 0 } }
http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24size
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