MongoDB Interview Question And Answers for 1 Year Experience

Question: How do I query mongodb with like ?
Following are few example of like as compare to SQL Query

/*select * from users where name like "%B%";*/
db.users.find({name: /B/});

/*select * from users where name like "B%"; */
db.users.find({name: /^B/});

/*select * from users where name like "%B"; */
db.users.find({name: /B$/});

Question: How to execute case in sensitive query?

/*select * from users where name like "%B%" OR like "%b%"; */
db.users.find({name: /b/i});

Question: How to list all collections in the mongoDB?
Following are three different methods.

db.getCollectionNames()

show collections

show tables

Question: Pretty print in MongoDB shell?
Normally we use query as below:

db.users.find()

For Pretty display, use like below:

db.users.find().pretty()

Question: How to get the last N records?

db.users.find().sort({_id:-1}).limit(20);
/* -1 means descending order */

Question: How to export collection into CSV?

mongoexport --host localhost --db bank --collection users --csv --out e:/dump/mycsv.csv --fields name,age,gender

Question: How to import into collection from CSV?

mongoimport -d bank -c users --type csv --file e:/dump/mycsv.csv --headerline

Question: How can I rename a field for all documents in MongoDB?

db.students.updateMany( {}, { $rename: { "name": "full_name" } } )

Question: How to store date/time in mongodb

db.users.insert({date: ISODate("2014-02-10T10:50:42.389Z")})

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MongoDB Cursor with Examples

Question: What is cursor in MongoDB?
Cursor is a pointer to the result set of a query.
When you run a query for documents we retrieve a pointer (cursor) to the results instead of all result return.


Question: Give example of Cursor?

var myCursor=db.users.find({"age":30});
while (myCursor.hasNext()) {
   print(tojson(myCursor.next()));
}

Question: How to get the data type of variable?

var data=10;
typeof data;

var data='10';
typeof data;

Output

number
string

Question: What is use of forEach with Cursor?
Iterates the cursor to each document.
Example 1

db.users.find({"age":30}).forEach(printjson);

Example 2

db.users.find({"age":30}).forEach(function(data){
    print(data.name);
});

Output

name1
name2
name3

Question: How to use limit with Query?

 
db.users.find({"age":30}).limit(5).pretty();

Now, cursor will return maximum 5 records.


Question: How to get results in Array instead of JSON?

 
db.users.find({"age":30}).toArray()

Question: How to get number of results from Query?

 
db.users.find({"age":30}).size(); //2

Question: How to sort records by name in Ascending order?

 
 db.users.find({"age":30}).sort({"name":1}).forEach(function(data){print(data.name);});

Question: How to sort records by name in Descending order?

 
 db.users.find({"age":30}).sort({"name":-1}).forEach(function(data){print(data.name);});

Question: How to skip 4th record from query?

 
 db.users.find({"age":30}).skip(4).forEach(function(data){print(data.name);});

Question: How to search records with indexing?

 
 db.users.find({"age":30}).hint({"age":1}).pretty();  

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