grouping mongo documents using elements of array field - mongodb

Question

I have below 3 documents. Each represents a contact for a user :
{
"_id" : ObjectId("57f9f9f3b91d070315273d0d"),
"profileId" : "test",
"displayName" : "duplicateTest",
"email" : [
{
"emailId" : "a#a.com"
},
{
"emailId" : "b#b.com"
},
{
"emailId" : "c#c.com"
}
]
}
{
"_id" : ObjectId("57f9fab2b91d070315273d11"),
"profileId" : "test",
"displayName" : "duplicateTest2",
"email" : [
{
"emailId" : "a#a.com"
}
]
}
{
"_id" : ObjectId("57f9fcefb91d070315273d15"),
"profileId" : "test",
"displayName" : "duplicateTest2",
"email" : [
{
"emailId" : "b#b.com"
}
]
}
I need to aggregate/group them by array elements so that I can identify the duplicate contact ( based on email id). Since there is a common email id between doc (1 & 2) and doc( 1 & 3) these 3 represent one contact and should be merged into one as one contact.
I tried doing this using $unwind and $group in java as below:
List<DBObject> aggList = new ArrayList<DBObject>();
BasicDBObject dbo = new BasicDBObject("$match", new BasicDBObject("profileId", "0fb72dcf-292b-4343-a0e7-1d613a803b1e"));
aggList.add(dbo);
BasicDBObject dboUnwind = new BasicDBObject("$unwind", "$email");
aggList.add(dboUnwind);
BasicDBObject dboGroup = new BasicDBObject("$group",
new BasicDBObject().append("_id", new BasicDBObject("name", "$email.emailId"))
.append("uniqueIds", new BasicDBObject("$addToSet", "$_id"))
.append("count", new BasicDBObject("$sum", 1)));
aggList.add(dboGroup);
BasicDBObject dboCount = new BasicDBObject("$match", new BasicDBObject("count", new BasicDBObject("$gte", 2)));
aggList.add(dboCount);
BasicDBObject dboSort = new BasicDBObject("$sort", new BasicDBObject("count",-1));
aggList.add(dboSort);
BasicDBObject dboLimit = new BasicDBObject("$limit", 10);
aggList.add(dboLimit);
AggregationOutput output = collection.aggregate(aggList);
System.out.println(output.results());
This groups docs by email id (and rightly so) but doesn't serves the purpose.
Any help would be highly appreciated.
I need to implement the feature where user can be prompted about the possible duplicate contacts in his repository. I need aggregation result to be something like:
[
{
"_id":{
"name":[
{
"emailId" : "a#a.com"
},
{
"emailId" : "b#b.com"
},
{
"emailId" : "c#c.com"
}
]
},
"uniqueIds":[
{
"$oid":"57f9fcefb91d070315273d15"
},
{
"$oid":"57f9fcefb91d070315273d11"
},
{
"$oid":"57f9fcefb91d070315273d15"
}
],
"count":3
},
So basically, I need _id for all possible duplicate contacts (there could be another group of duplicates with _ids list as above) so that I can prompt it to user and user can merge them at his will.
Hope its more clear now. Thanks!

Answer 1

Well your question differs a bit from the result you are seeking. Your inital question pointed me to the following aggregation:
db.table.aggregate(
[
{
$unwind: "$email"
},
{
$group: {
_id : "$email.emailId",
duplicates : { $addToSet : "$_id"}
}
}
]
);
This results in:
{
"_id" : "c#c.com",
"duplicates" : [
ObjectId("57f9f9f3b91d070315273d0d")
]
}
{
"_id" : "b#b.com",
"duplicates" : [
ObjectId("57f9fcefb91d070315273d15"),
ObjectId("57f9f9f3b91d070315273d0d")
]
}
{
"_id" : "a#a.com",
"duplicates" : [
ObjectId("57f9fab2b91d070315273d11"),
ObjectId("57f9f9f3b91d070315273d0d")
]
}
Grouped by EMail.
But the sample output you added to your question made this aggregation:
db.table.aggregate(
[
{
$unwind: "$email"
},
{
$group: {
_id : "$profileId",
emails : { $addToSet : "$email.emailId"},
duplicates : { $addToSet : "$_id"}
}
}
]
);
Which results in:
{
"_id" : "test",
"emails" : [
"c#c.com",
"b#b.com",
"a#a.com"
],
"duplicates" : [
ObjectId("57f9fcefb91d070315273d15"),
ObjectId("57f9fab2b91d070315273d11"),
ObjectId("57f9f9f3b91d070315273d0d")
]
}