Am really new to MongoDB or NoSQL database.
I have this userSchema schema
const postSchema = {
title: String,
posted_on: Date
}
const userSchema = {
name: String,
posts: [postSchema]
}I want to retrieve the posts by a user in given range(/api/users/:userId/posts?from=date&to=date&limit=limit) using mongodb query. In a relational database, we generally create two different sets of tables and query the second table(posts) using some condition and get the required result.
How can we achieve the same in mongodb? I have tried using $elemMatch by referring this but it doesn't seem to work.
2 ways to do it with aggregation framework, that can do much more than a find can do.
With find we mostly select documents from a collection, or project to keep some fields from a document that is selected, but here you need only some members of an array, so aggregation is used.
Local way (solution at document level) no unwind etc
Query
db.collection.aggregate([
{
"$match": {
"name": {
"$eq": "n1"
}
}
},
{
"$set": {
"posts": {
"$slice": [
{
"$filter": {
"input": "$posts",
"cond": {
"$and": [
{
"$gt": [
"$$this.posted_on",
1
]
},
{
"$lt": [
"$$this.posted_on",
5
]
}
]
}
}
},
2
]
}
}
}
])
Uwind solution (solution at collection level) (its smaller a bit, but keeping things local is better, but in your case it doesn't matter)
Query
db.collection.aggregate([
{
"$match": {
"name": {
"$eq": "n1"
}
}
},
{
"$unwind": {
"path": "$posts"
}
},
{
"$replaceRoot": {
"newRoot": "$posts"
}
},
{
"$match": {
"$and": [
{
"posted_on": {
"$gt": 1
}
},
{
"posted_on": {
"$lt": 5
}
}
]
}
},
{
"$limit": 2
}
])