Mongo groupby date inside array - mongodb

Question

I have collection in my db as,
[
{
"groupName" : "testName",
"participants" : [
{
"participantEmail" : "test#test.com",
"lastClearedDate" : 12223213123
},
{
"participantEmail" : "test2#test.com",
"lastClearedDate" : 1234343243423
}
],
"messages" : [
{
"message":"sdasdasdasdasdasd",
"time":22312312312,
"sender":"test#test.com"
},
{
"message":"gfdfvd dssdfdsfs",
"time":2231231237789,
"sender":"test#test.com"
}
]
}
]
This is a collection of group which contains all the participants and messages in that group.
The time field inside the message is Timestamp.
I want get all the messages inside a group which are posted after the given date and grouped by date.
I wrote the following code,
ChatGroup.aggregate([
{ $match: { group_name: groupName } },
{ $unwind: "$messages" },
{ $match: { "messages.time": { $gte: messagesFrom } } },
{
$project: {
_id: 0,
y: {
$year: {
$add: [new Date(0), { $multiply: [1000, "$messages.time"] }]
}
},
m: {
$month: {
$add: [new Date(0), { $multiply: [1000, "$messages.time"] }]
}
},
d: {
$dayOfMonth: {
$add: [new Date(0), { $multiply: [1000, "$messages.time"] }]
}
}
}
},
{
$group: {
_id: {
year: "$y",
month: "$m",
day: "$d"
},
messages: { $push: "$messages" },
count: { $sum: 1 }
}
}
]).then(
group => {
console.log("length of messages", group);
resolve(group);
},
err => {
console.log(err);
}
);
});
and I getting the following output,
[
{
"_id": {
"year": 50694,
"month": 9,
"day": 5
},
"messages": [],
"count": 3
},
{
"_id": {
"year": 50694,
"month": 8,
"day": 27
},
"messages": [],
"count": 1
},
{
"_id": {
"year": 50694,
"month": 8,
"day": 26
},
"messages": [],
"count": 10
}
]
I am not getting the messages but the count is correct.
Also the time which is displayed in the result is incorrect e.g. year, date and month.
Mongo version is 3.2.
I referred the groupby and push documentation from mongodb along with other stackoverflow questions on mongo group by.
What am I doing wrong?

Answer 1

Your timestamp is already in seconds. So, you don't need to convert them to millisecond by multiplying with 1000.
So your final query should be something like this
ChatGroup.aggregate([
{ "$match": {
"group_name": groupName,
"messages.time": { "$gte": messagesFrom }
}},
{ "$unwind": "$messages" },
{ "$match": { "messages.time": { "$gte": messagesFrom }}},
{ "$group": {
"_id": {
"year": { "$year": { "$add": [new Date(0), "$messages.time"] }},
"month": { "$month": { "$add": [new Date(0), "$messages.time"] }},
"day": { "$dayOfMonth": { "$add": [new Date(0), "$messages.time"] }}
},
"messages": { "$push": "$messages" },
"count": { "$sum": 1 }
}}
])

Answer 2

Add messages in $project
{
$project: {
_id: 0,
messages : 1,
.........
},
}