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
Check if a list is not empty in MongoDB?
For this, use the $size operator. Let us first create a collection with documents −
> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":["John","David"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cdd99e8bf3115999ed511f7")
}
> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":["Carol"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cdd99e9bf3115999ed511f8")
}
> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cdd99ebbf3115999ed511f9")
}
> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[null]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cdd99f2bf3115999ed511fa")
}
> db.checkIfListIsNotEmptyDemo.insertOne({"UserFriendGroup":[]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cdd99f6bf3115999ed511fb")
}Following is the query to display all documents from a collection with the help of find() method −
> db.checkIfListIsNotEmptyDemo.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5cdd99e8bf3115999ed511f7"),
"UserFriendGroup" : [
"John",
"David"
]
}
{
"_id" : ObjectId("5cdd99e9bf3115999ed511f8"),
"UserFriendGroup" : [
"Carol"
]
}
{ "_id" : ObjectId("5cdd99ebbf3115999ed511f9"), "UserFriendGroup" : [ ] }
{
"_id" : ObjectId("5cdd99f2bf3115999ed511fa"),
"UserFriendGroup" : [
null
]
}
{ "_id" : ObjectId("5cdd99f6bf3115999ed511fb"), "UserFriendGroup" : [ ] }Following is the query to check if a list is not empty −
> db.checkIfListIsNotEmptyDemo.find({'UserFriendGroup': {'$not': {'$size': 0}}});This will produce the following output −
{ "_id" : ObjectId("5cdd99e8bf3115999ed511f7"), "UserFriendGroup" : [ "John", "David" ] }
{ "_id" : ObjectId("5cdd99e9bf3115999ed511f8"), "UserFriendGroup" : [ "Carol" ] }
{ "_id" : ObjectId("5cdd99f2bf3115999ed511fa"), "UserFriendGroup" : [ null ] }
Updated on: 30-Jul-2019
313 Views
Advertisements