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 to fetch only the “Name” field based on roles?
For this, use aggregate(). Here, we have considered 3 roles − Admin, Guest, and User. Let us create a collection with documents −
> db.demo532.insertOne({"Name":"Chris","Type":"Admin"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4a9def4dcbee04fbbbf9")
}
> db.demo532.insertOne({"Name":"David","Type":"Guest"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4aa3ef4dcbee04fbbbfa")
}
> db.demo532.insertOne({"Name":"Bob","Type":"User"});{
"acknowledged" : true,
"insertedId" : ObjectId("5e8b4ab0ef4dcbee04fbbbfb")
}Display all documents from a collection with the help of find() method −
> db.demo532.find();
This will produce the following output −
{ "_id" : ObjectId("5e8b4a9def4dcbee04fbbbf9"), "Name" : "Chris", "Type" : "Admin" }
{ "_id" : ObjectId("5e8b4aa3ef4dcbee04fbbbfa"), "Name" : "David", "Type" : "Guest" }
{ "_id" : ObjectId("5e8b4ab0ef4dcbee04fbbbfb"), "Name" : "Bob", "Type" : "User" }Following is the query to get a unique document which needs to be compared with other documents in the same collection −
> db.demo532.aggregate([
... {$group: {_id:"$Name", "types":{$addToSet:"$Type"}}},
... {$project: {_id:1, "types": 1, "isSubset": { $setIsSubset: [ ["Admin"], "$types" ] }}},
... {$match: {"isSubset": false}},
... {$group: {_id:"$isSubset", "Name": {$push : "$_id"}}},
... {$project: {"_id": 0, "Name": 1}},
... {$unwind: "$Name"}
... ])This will produce the following output −
{ "Name" : "David" }
{ "Name" : "Bob" }
Updated on: 14-May-2020
192 Views
Advertisements