Count Documents in mongoose in single query - node.js

Question

const postsCount = await Post.find(query).countDocuments();
const allPosts = await Post.find(query)
.populate('likes')
.skip(startIndex)
.limit(noOfRecordsPerPage)
.sort({ createdAt: 'desc' });
I am querying two times in Database to find the total document count . How can i do this with a single query to the database ?

Answer 1

//you can use aggregation pipeline and $facet to combine two DB requests into one
//Actual Code output from windows Mongoshell/Command Line Interface(CLI)
> print("mongoDB",db.version())
mongoDB 4.2.6
> db.groups1.aggregate([
... {$facet:{
... "docCount":[
... {$group:{
... _id:null,
... count:{$sum:1}
... }
... }
... ],
... "allDocs":[
... {$match:{}}
... ]
... }
... }
... ]).pretty();
{
"docCount" : [
{
"_id" : null,
"count" : 4
}
],
"allDocs" : [
{
"_id" : ObjectId("5f817d142689512ef0bd3bd7"),
"uid" : 1,
"group_id" : "g1"
},
{
"_id" : ObjectId("5f817d142689512ef0bd3bd8"),
"uid" : 1,
"group_id" : "g2"
},
{
"_id" : ObjectId("5f817d142689512ef0bd3bd9"),
"uid" : 2,
"group_id" : "g2"
},
{
"_id" : ObjectId("5f817d142689512ef0bd3bd1"),
"uid" : 2,
"group_id" : "g3"
}
]
}
>

Answer 2

Use the $facet aggregation stage to combine multiple nested pipelines into your master pipeline.
Here's a working code of the above idea -
const countPipeline = [
{
$match: query
},
{
$group: {
_id: null,
count: {
$sum: 1
}
}
},
{
$project: {
_id: 0,
count: '$count'
}
}
];
const postPipeline = [
{
$match: query
},
{
$skip: startIndex
},
{
$limit: noOfRecordsPerPage
},
{
$sort: {
createdAt: -1
}
}
];
const pipeline = [
{
$facet: {
posts: postPipeline,
count: countPipeline
}
}
];
const results = await Posts.aggreagate(pipeline).exec();