Adding separate conditions for each item in Mongodb - mongodb

Question

I have 3 collections.
The user_movie collection keeps the relationship of the user and the movies he added to his list. The membership_date field is when the user is subscribed.
The user wants to see the reviews of the movies he added to his list.
But when showing these reviews, I want to show the comments after the subscription date.
With the query I tried, the user sees all the reviews.
Collection structure
db={
"user_movie": [
{
"_id" : 1,
"movie_id" : 1,
"user_id" : 1,
"status" : true,
"membership_date" : ISODate("2021-01-01")
},
{
"_id" : 2,
"movie_id" : 2,
"user_id" : 1,
"status" : true,
"membership_date" : ISODate("2021-01-01")
},
{
"_id" : 3,
"movie_id" : 3,
"user_id" : 1,
"status" : true,
"membership_date" : ISODate("2022-01-02")
}
],
"movie": [
{
"_id" : 1,
"movie_name" : "fugiat nulla",
},
{
"_id" : 2,
"movie_name" : "sint occaecat",
},
{
"_id" : 3,
"movie_name" : "cupidatat non",
}
],
"movie_reviews": [
{
"_id" : 1,
"movie_id" : 1,
"review": "Lorem ipsum dolor"
"review_date" : ISODate("2021-01-02"),
},
{
"_id" : 2,
"movie_id" : 2,
"review": "Consectetur adipiscing elit"
"review_date" : ISODate("2021-01-02"),
},
{
"_id" : 3,
"movie_id" : 3,
"review": "Do eiusmod tempor"
"review_date" : ISODate("2021-01-02"),
},
{
"_id" : 4,
"movie_id" : 3,
"review": "Abore et dolore magna"
"review_date" : ISODate("2022-01-01"),
}
]
}
The query I tried gives this output.
[
{
"_id" : 1,
"movie_id" : 1,
"date" : ISODate("2021-01-02"),
},
{
"_id" : 2,
"movie_id" : 2,
"date" : ISODate("2021-01-02"),
},
{
"_id" : 3,
"movie_id" : 3,
"date" : ISODate("2021-01-02"),
},
{
"_id" : 4,
"movie_id" : 3,
"date" : ISODate("2022-01-01"),
}
]
But this is not the output I was expecting. The movie reviews with id 3,4 should not be seen by the user. Because it was written before the membership_date date, so the user should not see these reviews.
How can I get all movie reviews of the user with id 1 as mentioned?

Answer 1

Stage 1: $lookup with pipeline
Join conditions:
By movie_id.
movie_review's review_date must not be earlier ($gte) than membership_date (from user_movie).
Stage 2: $unwind
Deconstruct movie_reviews array field to multiple document.
Stage 3: $replaceWith
Decorate the output document to show movie_review document.
db.user_movie.aggregate([
{
"$lookup": {
"from": "movie_reviews",
let: {
movie_id: "$movie_id",
membership_date: "$membership_date"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$movie_id",
"$$movie_id"
]
},
{
$gte: [
"$review_date",
"$$membership_date"
]
}
]
}
}
}
],
as: "movie_reviews"
}
},
{
$unwind: "$movie_reviews"
},
{
"$replaceWith": "$movie_reviews"
}
])
Sample Mongo Playground
Updated: Lookup join movie_reviews with user_movie
Since you are just to get movie_reviews, I think it is better to join from movie_reviews with user_movie instead of joining from user_movie with movie_reviews to get rid of the use of $unwind.
db.movie_reviews.aggregate([
{
"$lookup": {
"from": "user_movie",
let: {
movie_id: "$movie_id",
review_date: "$review_date"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$movie_id",
"$$movie_id"
]
},
{
$gte: [
"$$review_date",
"$membership_date"
]
}
]
}
}
}
],
as: "user_movie"
}
},
{
$match: {
"user_movie": {
$ne: []
}
}
},
{
$project: {
user_movie: 0
}
}
])
Sample Mongo Playground (Get movie_reviews)