How to group users data on mongo db - mysql

Question

I am trying to order the result from a monogo database, this is the equivalent in mysql.
SELECT * FROM `test` WHERE user1 = 'josieboy' or user2='josieboy' GROUP by user1, user2
This is my mongoDB query:
var query = Chat.aggregate(
{
$match:{
$or:[
{'user1':data},
{'user2':data}
]
}
},
{
$group : {
_id: '$user1',
receiver : { $first: '$user1' },
sender : { $first: 'user2' }
}
},
{
$project : {"_id":0, "user1":1, "user2":1}
}
);
The query returns more than the expected result :
RETURNED RESULT
id user1 user2 Message
1 fred josieboy HI
2 josieboy fred Wts up
3 racheal josieboy HI
EXPECTED RESULT
id user1 user2 Message
2 josieboy fred Wts up
3 racheal josieboy HIy
I would want to return a single match for Fred and Josieboy regardless of the number of rows returned and who is the user1 or user2 order by the latest id and latest message.
I would also be glad if the update query could be in mongodb ...
THanks

Answer 1

It's long and ugly but I think does what you want:
db.test.aggregate({
$match: {
$or: [{
'user1': data
}, {
'user2': data
}]
}
}, {
$project: {
user1: 1,
user2: 1,
Message: 1,
users: ["$user1", "$user2"]
}
}, {
$unwind: "$users"
}, {
$redact: {
$cond: {
if: {
$eq: ['$users', data]
},
then: '$$PRUNE',
else: '$$KEEP'
}
}
}, {
$group: {
_id: '$users',
__id: {
$last: '$_id'
},
user1: {
$last: '$user1'
},
user2: {
$last: '$user2'
},
Message: {
$last: '$Message'
}
}
}, {
$project: {
_id: '$__id',
user1: 1,
user2: 1,
Message: 1
}
})