MongoDB Online Quiz

Following quiz provides Multiple Choice Questions (MCQs) related to MongoDB Framework. You will have to read all the given answers and click over the correct answer. If you are not sure about the answer then you can check the answer using Show Answer button. You can use Next Quiz button to check new set of questions in the quiz.

Q 1 - The MongoDB explain() method does not support which of the following verbosity mode:

A - queryPlanner

B - executionStats

C - allPlansExecution

D - customExecutionStats

Answer : D

Explanation

The possible modes of explain() are: "queryPlanner", "executionStats", and "allPlansExecution".

Q 2 - Which of the following replica sets vote in the election of a primary replica set?

Answer : D

Explanation

All members of a replica set, unless the value of votes is equal to 0, vote in elections. This includes all delayed, hidden and secondary-only members.

Q 3 - Which of the following is the most important consideration while designing the schema for MongoDB?

A - The schema should match the data access and query patterns

B - The schema should be kept in 3NF similar to SQL schemas

C - The schema should focus on creating possible embedded documents

D - The schema should contain maximum indexes

Answer : A

Explanation

The efficiency of a MongoDB database depends on how well the database is designed depending on the application usage. The schema should be designed based on how the data access patterns are.

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 array ratings contains at least one element between 3 and 6?

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 } } } )

Answer : A

Explanation

$elemMatch operator is used to specify multiple criteria on the elements of an array such that at least one array element satisfies all the specified criteria.

Q 5 - You can implement a multi-document transaction in MongoDB using which of the following concept?

A - Tailable Cursor

B - Two Phase Commits

C - Compound Indexing

D - Multi Document Transaction is not supported by MongoDB

Answer : B

Explanation

Operations on a single document are always atomic with MongoDB databases; however, operations that involve multiple documents, which are often referred to as �multi-document transactions�, are not atomic.

Q 6 - Update If Correct is an approach for which of the following concepts in MongoDB:

A - Concurrency Control

B - Transaction Management

C - Atomicity

D - Performance Management

Answer : A

Explanation

The Update if Current pattern is an approach to concurrency control when multiple applications have access to the data.

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

Answer : A

Explanation

You have to give state and city as the key to group by and then calculate the sum of the population in each city.

Q 8 - In a replica set, a ________ number of members ensures that the replica set is always able to select a primary.

A - Odd

B - Even

C - Depends on the application architecture

D - 2

Answer : A

Explanation

An odd number of members ensures that the replica set is always able to elect a primary. If you have an even number of members, add an arbiter to get an odd number.

Q 9 - Which of the following operators can reverse the effects of a double unwind operation?

A - $push

B - $wind

C - $wind.$wind

D - Can�t be reversed.

Answer : A

Explanation

An unwind operation unwinds on an array field and creates separate documents. If you unwind it again same thing happens again. So if you had one document which had two arrays, the first array had 2 values and second array has 3 values. Unwinding this document two times will give 6 document. Now to combine them back, you can use the $push operator.

Q 10 - The ________ operator limits the contents of an array field from the query results to contain only the first element matching the query condition.

A - $

B - $elemMatch

C - $slice

D - An array cannot be retrieved element wise in MongoDB.

Answer : B

Explanation

The $elemMatch operator limits the contents of an array field from the query results to contain only the first element matching the $elemMatch condition.

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