MongoDB Online Quiz

Q 1 - Which of the following is correct explanation of MongoDB processes?

A - mongod.exe is the shell process and mongo.exe is the actual database process

B - mongo.exe is the shell process and mongod.exe is the actual database process

C - mongos.exe is the MongoDB server process needed to run database

D - mongodump.exe can be used to import database backup dump

Q 2 - Which of the following is true about sharding?

A - Sharding is enabled at the database level

B - Creating a sharded key automatically creates an index on the collection using that key

C - We cannot change a shard key directly/automatically once it is set up

D - A sharded environment does not support sorting functionality since the documents lie on various mongod instances

Q 3 - Which of the following commands can cause the database to be locked?

A - Issuing a query

B - Inserting data

C - Map-reduce

D - All of the above

Q 4 - Consider that the posts collection contains an array called ratings which contains ratings given to the post by various users in the following format:

{
         _id: 1,
         post_text: “This is my first post”,
         ratings: [5, 4, 2, 5],
         //other elements of document 			
}

Which of the following query will return all the documents where the ratings array contains elements that in some combination satisfy the query conditions?

A - db.inventory.find( { ratings: { $elemMatch: { $gt: 3, $lt: 6 } } } )

B - db.inventory.find( { ratings: { ratings: { $gt: 5, $lt: 9 } } } )

C - db.inventory.find( { ratings: { ratings.$: { $gt: 5, $lt: 9 } } } )

D - db.inventory.find( { ratings: { $elemMatch: { $gte: 3, $lte: 6 } } } )

Q 5 - Consider the following posts document:

{
 	_id: 1,
	post_text: “This is my first post”,
	author: “Tom”,
	tags: [“tutorial”,”quiz”,”facebook”,”learning”,”fun”]
}

Which of the following queries will return the documents but with only the first two tags in the tags array?

A - db.posts.find({author:"Tom"},{tags:{$slice:2}})

B - db.posts.find({author:"Tom"}).limit({tags:2})

C - db.posts.find({author:"Tom"}).limit($slice:{tags:2})

D - Both a and c are valid. $slice works both with projection and limit.

Q 6 - What is the equivalent command in MongoDB for the following SQL query?

SELECT * FROM posts WHERE author like "%john%"

A - db.posts.find( { author: /john/ } )

B - db.posts.find( { author: {$like: /john/} } )

C - db.posts.find( { $like: {author: /john/} } )

D - db.posts.find( { author: /^john^/ } )

Q 7 - Consider that you have a collection called population which has fields state and city. Which of the following query will calculate the population grouped by state and city?

A - db.population.aggregate( [{ $group: { _id: { state: "$state", city: "$city" },pop: { $sum: "$pop" } } }] )

B - db.population.aggregate( [{ $group: { _id: { state: "$state", city: "$city" },pop: { $sum: 1 } } }] )

C - db.population.aggregate( [{ $group: { _id: { state: "$state", city: "$city" },pop: { “$pop”: 1 } } }] )

D - db.population.aggregate( [{ $group: { _id: { city: "$city" },pop: { $sum: "$pop" } } }] )Multi Document Transaction is not supported by MongoDB

Q 8 - What is a replica set node which does not maintain its own data but exists only for voting purpose called?

A - Secondary

B - Arbiter

C - Delayed

D - Hidden

Q 9 - Consider that you have the following two documents in the products collection:

{ "_id" : 1, "prices" : [ 60, 100, 200 ] }

{ "_id" : 2, "prices" : [ 20, 90, 150 ] }

What will the following query result into:

db.products.update(
   { _id: 1, prices: 100 },
   { $set: { "prices.$" : 111 } }
)

A - Updates 60 to 100

B - Updates 100 to 111

C - Updates 60,100 and 200 to 111

D - Removes the three elements of the prices array and replaces it with only a single element 111

Q 10 - Consider the following document from the products collection:

{
 _id: 1,
 product_code: "345678",
 variations: [
              { size: "L", price: 1000 },
              { size: "M", price: 800 }
           ]
}

What does the following query using $elemMatch return?

db.products.find( { product_code: "345678" },
                 { variations: { $elemMatch: { size: “L” } } } )

A - Returns the complete document since MongoDB does not support partial array retrieval

B - Returns the document but with only one element in the variations array (corresponding to size L)

C - Returns the complete document but retrieves only the size field from the array

D - Returns the complete document but retrieves only the size field from the array and also with only one element in the variations array (corresponding to size L)