How to match by 'undefined' value in MongoDB Aggregation Framework?
If you want to filter out documents that have some fields missing, use the $exists
operator.
This works on my machine :
> db.test.drop()
true
> db.test.insert( {'Hello':'World!', 'myField':42})
> db.test.insert( {'Hello again':'World!'})
> db.test.aggregate({'$match':{ 'myField':{'$exists':false} }})
{
"result" : [
{
"_id" : ObjectId("51b9cd2a6c6a334430ec0c98"),
"Hello again" : "World!"
}
],
"ok" : 1
}
The document that has myField present does not show in the results.
Filter it by $type:6
, (mongodb referece, note that this type marked as 'deprecated'):
db.records.aggregate({
$match: {
myField: {'$type':6},
}
})
If you have fields that exist but are undefined you can search for them with null.
db.records.aggregate({
$match: {
myField: {$exists: true, $eq: null},
}
})