Get all the distinct users through mongodb aggregation - mongodb

Question

I have an collection for messages something like below. Now i want to get all the distinct users to which ObjectId("57f55e4799aabf1c0565bc10") messages or receive message excluding itself (ObjectId("57f55e4799aabf1c0565bc10")). So how i can achieve it using aggregation.
/* 1 */
{
"_id" : ObjectId("57f55e0199aabf1c0565bc0e"),
"message" : "fghjfghj",
"to" : ObjectId("57f54e154df8d0193577889a"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:09:37.307Z"),
"createdDate" : ISODate("2016-10-05T20:09:37.307Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 2 */
{
"_id" : ObjectId("57f55e2d99aabf1c0565bc0f"),
"message" : "ghjkfhkg",
"to" : ObjectId("57f54e154df8d0193577889a"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:10:21.245Z"),
"createdDate" : ISODate("2016-10-05T20:10:21.245Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 3 */
{
"_id" : ObjectId("57f55e4799aabf1c0565bc10"),
"message" : "hgkgh",
"to" : ObjectId("57f54e154df8d0193577889a"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:10:47.614Z"),
"createdDate" : ISODate("2016-10-05T20:10:47.614Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 4 */
{
"_id" : ObjectId("57f55e7199aabf1c0565bc11"),
"message" : "cbjngcfj",
"to" : ObjectId("57f54e154df8d0193577889a"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:11:29.197Z"),
"createdDate" : ISODate("2016-10-05T20:11:29.197Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 5 */
{
"_id" : ObjectId("57f5801d94ef64d760275368"),
"message" : "cbjngcfj",
"from" : ObjectId("57f54e154df8d0193577889a"),
"to" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:11:29.197Z"),
"createdDate" : ISODate("2016-10-05T20:11:29.197Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 6 */
{
"_id" : ObjectId("57f5865494ef64d76027536a"),
"message" : "hgkgh",
"to" : ObjectId("57f54e154df8d0193577889b"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-05T20:10:47.614Z"),
"createdDate" : ISODate("2016-10-05T20:10:47.614Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 7 */
{
"_id" : ObjectId("57f666de7d13f10b5aa53527"),
"message" : "Zsdfsdf",
"to" : ObjectId("57f54dd36df11022ac5d7769"),
"from" : ObjectId("57f54dd36df11022ac5d7769"),
"modifiedDate" : ISODate("2016-10-06T14:59:42.943Z"),
"createdDate" : ISODate("2016-10-06T14:59:42.943Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 8 */
{
"_id" : ObjectId("57f667397d13f10b5aa53528"),
"message" : "HIIIIIIIIIIIII",
"to" : ObjectId("57f54dd36df11022ac5d7769"),
"from" : ObjectId("57f54dd36df11022ac5d7769"),
"modifiedDate" : ISODate("2016-10-06T15:01:13.993Z"),
"createdDate" : ISODate("2016-10-06T15:01:13.993Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
/* 9 */
{
"_id" : ObjectId("57f66972a533c40d67ebfab8"),
"message" : "gfjghk",
"to" : ObjectId("57f54e154df8d0193577889a"),
"from" : ObjectId("57f5522099aabf1c0565bbfe"),
"modifiedDate" : ISODate("2016-10-06T15:10:42.721Z"),
"createdDate" : ISODate("2016-10-06T15:10:42.721Z"),
"isDeleted" : false,
"status" : true,
"type" : "Message",
"__v" : 0
}
I have tried but didn't able to get the required result as below :
db.getCollection('conversations').aggregate([
{$match : {'type' : 'Message',
$or : [
{from : ObjectId("57f5522099aabf1c0565bbfe")},
{to : ObjectId("57f5522099aabf1c0565bbfe")}
]
}
},
{ $group: {_id : {"to" : "$to", 'from':"$from" }}},
]);
Expecting results like : -
[
ObjectId("57f54e154df8d0193577889a")
ObjectId("57f54e154df8d0193577889b")
]
Thanks for any suggestion.

Answer 1

You can use the $addToSet to add the senders and receivers to their respective sets(lists). Then you can use $setUnion to combine the sets. Then, you can use $setDifference to remove the current user.
db.getCollection('conversations').aggregate([
{$match : {'type' : 'Message',$or : [ {from : ObjectId("57f5522099aabf1c0565bbfe")},
{to : ObjectId("57f5522099aabf1c0565bbfe")}]}},
{ $group: {_id : null, from : {"$addToSet" : "$from"}, to : {"$addToSet" : "$to"}}},
{"$project":{"userAll":{"$setUnion":["$from", "$to"]}}},
{"$project":{"_id":0, users: {"$setDifference":["$userAll", [ObjectId("57f5522099aabf1c0565bbfe")]]}}}
]);
Sample output:
{
"users" : [
ObjectId("57f54e154df8d0193577889b"),
ObjectId("57f54e154df8d0193577889a")
]
}