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 query for capped sub-collection in an array
In MongoDB, you cannot use capped for sub-collection. However, use capped on the overall document. To display a specific number of values from an array, prefer $slice.
Let us create a collection with documents −
> db.demo319.insertOne({"Scores":[100,345,980,890]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50ecf6f8647eb59e562064")
}
> db.demo319.insertOne({"Scores":[903,10004,84575,844]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e50ed01f8647eb59e562065")
}Display all documents from a collection with the help of find() method −
> db.demo319.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5e50ecf6f8647eb59e562064"),
"Scores" : [
100,
345,
980,
890
]
}
{
"_id" : ObjectId("5e50ed01f8647eb59e562065"),
"Scores" : [
903,
10004,
84575,
844
]
}Following is the query for capped sub-collection in an array −
> db.demo319.aggregate([
... { $project: {TwoScores: { $slice: [ "$Scores", 2 ] } } }
... ])This will produce the following output −
{ "_id" : ObjectId("5e50ecf6f8647eb59e562064"), "TwoScores" : [ 100, 345 ] }
{ "_id" : ObjectId("5e50ed01f8647eb59e562065"), "TwoScores" : [ 903, 10004 ] }
Updated on: 02-Apr-2020
316 Views
Advertisements