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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 - Consider a collection posts which has fields: _id, post_text, post_author, post_timestamp, post_tags etc. Which of the following query retrieves ONLY the key named post_text from the first document retrieved?

A - db.posts.find({},{_id:0, post_text:1})

B - db.posts.findOne({post_text:1})

C - db.posts.finOne({},{post_text:1})

D - db.posts.finOne({},{_id:0, post_text:1})

Answer : D

Explanation

By default, MongoDB returns the _id field with each document. So in case you want ONLY the post_text field, you will have to exclude the _id field explicitly. Also, since we have to retrieve only the first document we have to use findOne and not find.

Q 2 - What is the output of the following program?

Answer : A

Explanation

In the default configuration, MongoDB writes data to the main data files on disk every 60 seconds.

Q 3 - What does the following MongoDB command return?

db.posts.find( { likes : { $gt : 100 }, likes : { $lt : 200 } } );

A - Posts with likes greater than 100 but less than 200

B - Posts with likes greater than or equal to 100 but less than or equal to 200

C - Posts with likes less than 200

D - Will return syntax error

Answer : C

Explanation

When the mongo shell interprets this query, it will override the first condition $gt and consider only the $lt one. To apply both the less than and greater than condition, you will have to use the $and operator.

Q 4 - Consider that you are using { upsert : true } option in your update command. Which of the following parameters will be used to determine if any new documents were inserted:

Answer : D

Explanation

The nUpserted shows the number of documents that were added during the update operation.

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 - Which of the following is not a system collection in MongoDB?

A - database.system.indexes

B - database.system.namespaces

C - admin.system.users

D - admin.system.preferences

Answer : D

Explanation

There is no system collection to store database preferences.

Q 7 - What does the output x of the following MongoDB aggregation query result into:

db.posts.aggregate( [ { $group: { _id: "$author", x: { $sum: $likes } } } ] )

A - Average of likes on all the posts of an author, grouped by author

B - Number of posts by an author

C - Sum of likes on all the posts by an author, grouped by author

D - Sum of likes on all the posts by all the authors

Answer : C

Explanation

The above query first does a grouping on author field and then calculates the number of likes on all the posts that were grouped together.

Q 8 - Which of the following command is used to get all the indexes on a collection?

A - db.collection.getIndexes()

B - db.collection.showIndexes()

C - db.collection.findIndexes()

D - db.showIndexes()

Answer : A

Explanation

db.collection.getIndexes() is the correct choice.

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

Answer : B

Explanation

All replica set members contain a copy of the oplog, in the local.oplog.rs collection, which allows them to maintain the current state of the database.

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)

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