How to combined two output in lambda function using mongodb? - mongodb

Question

I have two collection 1) profile ,2) posts find the below pic for your reference. user_prfoile collection
user_posts collection
In the lambda function, when i passed the userid, then we will get the userid revlevant data display. but i need user details in feelings array.
I tried with the below code, but i get the empty output
def lambda_handler(event, context):
print("Received event: " + json.dumps(event, indent=1))
Userid = event['userid']
uid = ObjectId(Userid)
dispost = list( db.user_posts.aggregate([{ "$match" : { "userid" : uid } },
{ "$unwind" : "$user_profile" },
{"$lookup":
{
"from" : 'user_profile',
"localField" : 'feelings.userid',
"foreignField" : '_id',
"as" : 'user_details'
}
},
{ "$addFields" : { "user_details.feelings.username" : "$user_profile.username", "user_details.feelings.photo" : "$user_profile.photo"}},
{ "$group" : {
"_id" : "$_id",
"user_profile" : {
"$push" : {
"$arrayElemAt" : ["$user_details", 0]
}}}},
{ "$project" : { "_id" : "$_id", "userid" : 1, "type" : 1, "feelings" : 1 }}
]))
disair = json.dumps(dispost, default=json_util.default)
return json.loads(disair)
I get an empty output.
I need output like this below.
_id :
userid :
type :
location :
feelings :
[ {userid : objectid(""),
username : "nipun",
photo : " "},
{userid : objectid(""),
username : "ramesh",
photo : " "}
]
in feelings array , i need user details from user_profile collection based on userid in feelings array.

Answer 1

Ok, there are couple of issues with that aggregation query, keeping most of it as is, I've modified it to work, as of now please try this and make any changes needed :
db.getCollection('user_posts').aggregate([{ "$match": { "userid": uid } },
{ "$unwind": "$feelings" },
{
"$lookup":
{
"from": 'user_profile',
"localField": 'feelings.userid',
"foreignField": '_id',
"as": 'feelings'
}
},
{
"$group": {
"_id": "$_id", userPost: { "$first": "$$CURRENT" }, "feelings": {
"$push": { "$arrayElemAt": ["$feelings", 0] }
}
}
}, { "$project": { userid: '$userPost.userid', type: '$userPost.type', "feelings": 1 } }
])