MongoDB Online Quiz


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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.

Questions and Answers

Answer : C

Explanation

$set is used to set the value of a particular field in a document. The syntax of set is $set:{column_name : column_value}. Also, {multi:true} is needed to update all the documents. Otherwise only the first found document is updated.

Q 2 - Which of the following command can be used in mongo shell to show all the databases in your MongoDB instance?

A - show dbs

B - show databases

C - show dbs -all

D - ls dbs

Answer : A

Explanation

show dbs returns the list of all the databases.

Answer : A

Explanation

The $gt, $lt and related operators can be applied for string manipulations too. They work in the same manner as they would work on numeric values.

Answer : C

Explanation

You cannot insert two documents with the same _id field. The value of _id field should be unique.

Q 5 - Which type of indexes does MongoDB support?

A - Compound Indexes

B - Multikey Indexes

C - Geospatial Indexes

D - All of the above

Answer : D

Explanation

MongoDB supports all of the above mentioned indexes.

Answer : A

Explanation

When you have a sequence with $sort followed by a $match, the $match moves before the $sort to minimize the number of objects to sort.

Q 7 - The following aggregation option is used to specify the specific fields that needs to be passed to the next stage of the aggregation pipeline:

A - $match

B - $project

C - $group

D - $aggregate

Answer : B

Explanation

The $project operator passes along the documents with only the specified fields to the next stage in the pipeline. The specified fields can be existing fields from the input documents or newly computed fields.

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

Answer : A

Explanation

Deconstructs an array field from the input documents to output a document for each element. Each output document is the input document with the value of the array field replaced by the element.

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.


mongodb_questions_answers.htm

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