MongoDB Online Quiz

Q 1 - Which of the following MongoDB query is equivalent to the following SQL query:

UPDATE users SET status = "C" WHERE age > 25

A

db.users.update(
   { age: { $gt: 25 } },
   { status: "C" })

B

db.users.update(
 { age: { $gt: 25 } },
 { $set: { status: "C" } })

C

db.users.update(
 { age: { $gt: 25 } },
 { $set: { status: "C" } },
 { multi: true })

D

db.users.update(
 { age: { $gt: 25 } },
 { status: "C" },
 { multi: true })

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 - In our posts collection, which command can be used to find all the posts whose author names begin lie between “A” and “C” in dictionary order?

A - db.posts.find( { post_author : { $gte : "A" , $lte : "C" } } );

B - db.posts.find( { post_author : { $gte : "C" , $lte : "A" } } );

C - db.posts.find( { post_author : { $gt : "A" , $lt : "C" } } );

D - This type of search is not supported by MongoDB. $lt and $gt operators are applicable only for numeric values.

Q 4 - What does the following query do when performed on the posts collection?

db.posts.update({_id:1},{Title:This is post with ID 1"})

A - Updates the Title of the post

B - Updating a document is possible only with $set

C - Replaces the complete document with _id as 1 with the document specified in second parameter

D - Syntax error

Q 5 - What does the totalKeysExamined field returned by the explain method indicate?

A - Number of documents that match the query condition

B - Number of index entries scanned

C - Number of documents scanned

D - Details the completed execution of the winning plan as a tree of stages

Q 6 - Which of the following collections are used by MongoDB to store GridFS data?

A - fs.files and fs.chunks

B - fs.grid and fs.chunks

C - fs.parts and fs.files

D - fs.chunks and fs.parts

Q 7 - What is the minimum sensible number of voting nodes to a replica set?

A - 2

B - 3

C - 4

D - 5

Q 8 - Given the following posts document:

{
 "_id" : 1, 
 "post_text" : "This post does not matter”, 
  “tags”: [ "tutorial", "fun", "learning"],
  // rest of the document
}

What will be the output of following query:

db.posts.aggregate( [ { $unwind : "$tags" } ] )

A - Return three separate documents for three separate tags

B - Arranges the tags (wind) in ascending order

C - Arranges the tags (wind) in descending order

D - Returns one document but converts the tags array in an object

Q 9 - The oplog (operations log) is a special capped collection that keeps a rolling record of all operations that modify the data stored in your databases. All the replica set members contain a copy of the oplog in the following collection:

A - oplog.rs

B - local.oplog.rs

C - <database>..oplog.rs

D - <replicasetid>.oplog.rs

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)