30 Important Questions for MongoDB Interview

1. To create database: $ use < Database-name >
   
   
2. To check current database: DB
   
   
3. Use database by creating a user
   $ db.createuser({user : “root”, pwd : “123”, roles : [“readwrite, “dbAdmin”] }):
   
   
4.  Create collection:
   $ db.createCollection (‘collection_name’);
   
   
5. insert data:
   $db.customers.insert({first_name:”ABC”,last_name:”doe”});
   
   
6. Show record:
   $db.colection_name.find( );
   
7. Add multiple record using array
   $db.customer.insert([{ first_name: ‘Albert’, last_name : ‘Einstein’},{
   fisrt_name: ‘smith’, last_name: “xyz”}]);
   
   
8. Update in mongoDB
   syntax: db.collection.update({matches}, {what to replace});

db.customers.update({first_name: “smith”}, {first_name: ” smith”,
last_name : “Doe”, gender: “male”});

It will replace the whole record that matches with first_name smith. Also, if we notice previous query, we were passing first_name and last_name along with the gender, you might have thought we could have done something like below;
$ db.customers.update ({first_name : “smith”}, {gender: “male”}):

But by doing this, this will replace the complete document of your matches.

Now if you retrieve the data then you will just find { gender: “male”}. You will lose first_name and last_name.

Solution: db.customers.update ({ first_name : “Steve},{$ set:{ gender “male”}});