mongodb aggregation with array and lookup - mongodb

Question

I have a MongoDB collection with documents in the following format
collection name called post
{
"_id" : ObjectId("5c88b225fac24431d947abad"),
"user_id" : "5c87ad6c623f1e2bd4d041d0",
"post_likes" : [
{
"post_user_id" : "5c87ad6c623f1e2bd4d041d0",
"like_status" : true
},
{
"post_user_id" : "5c88b42b71611926c055508b",
"like_status" : true
}
],
"post_comments" : [
{
"comment_user_id" : "5c87ad6c623f1e2bd4d041d0",
"comment_like" : "",
"comment_description" : ""
},
{
"comment_user_id" : "5c88b42b71611926c055508b",
"comment_like" : "",
"comment_description" : "nice post"
}
]
}
i have another collection name called user_ptofile_info
{
"_id" : ObjectId("5c923682c088564cf01056cb"),
"user_id" : "5c87ad6c623f1e2bd4d041d0",
"image_url" : "image/url",
"user_name":"xxxxxxxx",
"created_at" : "",
"updated_at" : ""
}
requested output like
note:the post_user_id from user_ptofile_info and user_id from post are lookup and i need total count for post_likes and post comments also
{
"_id" : ObjectId("5c88b225fac24431d947abad"),
"user_id" : "5c87ad6c623f1e2bd4d041d0",
"post_likes" : [
{
"post_user_id" : "5c87ad6c623f1e2bd4d041d0",
"like_status" : true,
"image_url" : "image/url",
"user_name":"xxxxxxxx",
},
{
"post_user_id" : "5c88b42b71611926c055508b",
"like_status" : true,
"image_url" : "image/url",
"user_name":"xxxxxxxx",
}
],
"post_comments" : [
{
"comment_user_id" : "5c87ad6c623f1e2bd4d041d0",
"comment_like" : "",
"comment_description" : ""
},
{
"comment_user_id" : "5c88b42b71611926c055508b",
"comment_like" : "",
"comment_description" : "nice post"
}
]
}

Answer 1

You can use below aggregation:
db.post.aggregate([
{
$lookup: {
from: "user_profile_info",
let: { user_ids: "$post_likes.post_user_id" },
pipeline: [
{ $match: { $expr: { $in: [ "$user_id", "$$user_ids" ] } } },
{
$project: {
post_user_id: "$user_id",
image_url: 1,
user_name: 1
}
}
],
as: "users"
}
},
{
$project: {
_id: 1,
user_id: 1,
post_likes: {
$map: {
input: "$users",
as: "user",
in: {
post_user_id: "$$user.post_user_id",
image_url: "$$user.image_url",
user_name: "$$user.user_name",
like_status: {
$let: {
vars: {
like: {
$arrayElemAt: [
{ $filter: { input: "$post_likes", as: "pl", cond: { $eq: [ "$$pl.post_user_id", "$$user.post_user_id" ] } } }, 0
]
}
},
in: "$$like.like_status"
}
}
}
}
},
post_comments: 1
}
}
])
$lookup with custom pipeline (MongoDB 3.6 or newer) will allow you to get the data from user_profile_info for all users that are present in post_likes array. Then you need to "merge" users array with post_likes to get like_status. Since you have two arrays and you know that the same post_user_id appears in both of them you can use $map with $arrayElemAt and $filter to combine the data from both arrays.