Node.js and MongoDB Solved Interview Problem (Oct 2022)

Question:

I'm making 2 queries (or a single query) to the database. 
What I want to achieve:

If one of them is null, I want to add the value 'nil'. Example:

field1: nil,
field2: 'value'

If both are null, then I want it to respond with the 'not found' message.

What's a good approach for this?

Answer:

First, we setup the local database.


Running a local instance

(base) ashish@ashishlaptop:~/Desktop$ mongosh
Current Mongosh Log ID:	63498870b0f4b94029f7b626
Connecting to:		mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+1.6.0
Using MongoDB:		6.0.2
Using Mongosh:		1.6.0

For mongosh info see: https://docs.mongodb.com/mongodb-shell/


To help improve our products, anonymous usage data is collected and sent to MongoDB periodically (https://www.mongodb.com/legal/privacy-policy).
You can opt-out by running the disableTelemetry() command.

------
   The server generated these startup warnings when booting
   2022-10-14T21:33:50.958+05:30: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
   2022-10-14T21:33:52.643+05:30: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
   2022-10-14T21:33:52.644+05:30: vm.max_map_count is too low
------

------
   Enable MongoDB's free cloud-based monitoring service, which will then receive and display
   metrics about your deployment (disk utilization, CPU, operation statistics, etc).
   
   The monitoring data will be available on a MongoDB website with a unique URL accessible to you
   and anyone you share the URL with. MongoDB may use this information to make product
   improvements and to suggest MongoDB products and deployment options to you.
   
   To enable free monitoring, run the following command: db.enableFreeMonitoring()
   To permanently disable this reminder, run the following command: db.disableFreeMonitoring()
------

test> 
test> db
test
test> show dbs

admin   40.00 KiB
config  12.00 KiB
local   72.00 KiB  

test> 

test> 

test> db.createCollection("ccn1")
{ ok: 1 }

test> db.ccn1.insertOne({"name":"Ashish Jain","address":"Delhi"})

{
  acknowledged: true,
  insertedId: ObjectId("634989627d163a41b75e1e13")
}
test> 

Next Command

db.ccn1.insertMany([  
  {"name":"","address":"India"},
  {"name":"","address":""},
  {"name":"Ash","address":""}
])


test> db.ccn1.insertMany([  
... {"name":"","address":"India"},
... {"name":"","address":""},
... {"name":"Ash","address":""}
... ])

{
  acknowledged: true,
  insertedIds: {
    '0': ObjectId("634989cc7d163a41b75e1e14"),
    '1': ObjectId("634989cc7d163a41b75e1e15"),
    '2': ObjectId("634989cc7d163a41b75e1e16")
  }
}
test> 

Our Database Looks Like This

[
  {
    _id: new ObjectId("634989627d163a41b75e1e13"),
    name: 'Ashish Jain',
    address: 'Delhi'
  },
  {
    _id: new ObjectId("634989cc7d163a41b75e1e14"),
    name: '',
    address: 'India'
  },
  {
    _id: new ObjectId("634989cc7d163a41b75e1e15"),
    name: '',
    address: ''
  },
  {
    _id: new ObjectId("634989cc7d163a41b75e1e16"),
    name: 'Ash',
    address: ''
  }
]
 
This is our Node.js code in file "script.js"


var MongoClient = require('mongodb').MongoClient;

var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  var dbo = db.db("test");
  var all_docs = dbo.collection("ccn1").find({}).toArray(function(err, result) {
    if (err) throw err;
    
    
    for (i in result){
        if(result[i]['name'] && result[i]['address']) {
            console.log("name: " + result[i]['name'])
            console.log("address: " + result[i]['address'])
        }

        else if (result[i]['name'] && !result[i]['address']){
            console.log("name: " + result[i]['name'])
            console.log("address: nil")
        }

        else if (!result[i]['name'] && result[i]['address']){
            console.log("name: nil")
            console.log("address: " + result[i]['address'])
        }

        else {
            console.log("Not Found")
        }

        console.log()
        
    }

    db.close();
  });
});  

This is our output


(base) ashish@ashishlaptop:~/Desktop/software/node$ node script.js 
name: Ashish Jain
address: Delhi

name: nil
address: India

Not Found

name: Ash
address: nil  

Tags: Technology,Database,JavaScript,