Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
MongoDB Aggregation to slice array inside array
For this, use aggregate() in MongoDB. In that, use $slice to slice array inside array. Let us create a collection with documents −
> db.demo111.insertOne(
... {
... "_id" : 101,
... "Name" : "Chris",
... "Details" : [
... {
... "_id" : 101,
... "Score" : 78,
... "Subjects" : [
... {
... "_id" : "10001",
... "SubjectName" : "MySQL"
... },
... {
... "_id" : "10003",
... "SubjectName" : "MongoDB"
... }
... ]
... },
... {
... "_id" : 102,
... "Score" : 87,
... "Subjects" : [
... {
... "_id" : "10004",
... "SubjectName" : "Java"
... }
... ]
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 101 }Display all documents from a collection with the help of find() method −
> db.demo111.find();
This will produce the following output −
{
"_id" : 101, "Name" : "Chris", "Details" : [
{ "_id" : 101, "Score" : 78, "Subjects" : [ { "_id" : "10001", "SubjectName" : "MySQL" },
{ "_id" : "10003", "SubjectName" : "MongoDB" } ] },
{ "_id" : 102, "Score" : 87, "Subjects" : [ { "_id" : "10004", "SubjectName" : "Java" } ] }
]
}Following is the query to slice array inside array −
> db.demo111.aggregate([
... { "$addFields": {
... "Details": {
... "$map": {
... "input": "$Details",
... "as": "out",
... "in": {
... "_id": "$$out._id",
... "Score": "$$out.Score",
... "Subjects": { "$slice": [ "$$out.Subjects", 1 ] }
... }
... }
... }
... }}
... ])This will produce the following output −
{
"_id" : 101, "Name" : "Chris", "Details" : [
{ "_id" : 101, "Score" : 78, "Subjects" : [ { "_id" : "10001", "SubjectName" : "MySQL" } ] },
{ "_id" : 102, "Score" : 87, "Subjects" : [ { "_id" : "10004", "SubjectName" : "Java" } ] }
]
}
Updated on: 30-Mar-2020
266 Views
Advertisements