How to query items in array alone in Mongodb - mongodb

Question

My collection name is employee and my collections as follows
{
"Title":"IssueFixingTeam",
"TeamLead":"Mr.Bean",
"workers":["xxx","yyy","zzz"]
},
{
"Title":"DevelopmentTeam",
"TeamLead":"Mr.John Doe",
"workers":["aa","dd","ss"]
}
how to query to find, how many workers are there under TeamLead "Mr.Bean"
Thanks in advance

Answer 1

if you are interested in just one record (otherwise, see the answer by #felix) belonging to "Mr.Bean", then this could give you the required count:
db.employee.findOne({'TeamLead': 'Mr.Bean'}).workers.length

Answer 2

Use Match
to filter TeamLead: Mr.Bean
use Size operator in Project
to get size of array,
db.collection.aggregate([{
$match: {
TeamLead: "Mr.Bean"
}
}, {
$project: {
"TeamLead":1,
workers: {
$size: "$workers"
}
}
}])

Answer 3

You can use the aggregation framework.
In case you are only interested in matching documents of a specific TeamLead and sum per document:
db.foo.aggregate([{$match: {"TeamLead": "Mr.Bean"}},
{$project: {"num_workers": {$size: "$workers"}}}])
Output:
{ "_id" : ObjectId("58c6a5ef9bc86fa5c7e4fa50"), "num_workers" : 3 }
If you want to group documents by TeamLead and get the number of unique workers under each TeamLead:
db.foo.aggregate([{$group: {"_id": "$TeamLead", "workers": {$addToSet: "$workers"}}},
{$unwind: "$workers"},
{$project: {"num_workers": {$size: "$workers"}}}])
Output:
{ "_id" : "Mr.John Doe", "num_workers" : 3 }
{ "_id" : "Mr.Bean", "num_workers" : 3 }