The Best MongoDB C100DEV Study Guides and Dumps of 2024 [Q91-Q113]

QUESTION 91
The users collection in the database is given. Which field will be the best candidate for an index in terms of cardinality?

gender (low cardinality)

age (medium cardinality)

email (high cardinality)

QUESTION 92
What is a MongoDB view?

MongoDB does not support views.

A MongoDB view is a queryable object whose contents are defined by an aggregation pipeline on other collections or views.

It is a different name for collection.

QUESTION 93
Which of the following documents are valid JSON format? (select 2)

{_id: 1, name: “Riviera Caterer”, cuisine: “American”}

<“_id”: 1, “name”: “Riviera Caterer”, “cuisine”: “American”>

[“_id”: 1, “name”: “Riviera Caterer”, “cuisine”: “American”]

{“_id”: 1, “name”: “Riviera Caterer”, “cuisine”: “American”}

{“_id”: 1, “address”: {“street”: “Stillwell Avenue”, “zipcode”: “11224”}}

QUESTION 94
Suppose you have a companies collection in your database. Only the following documents are stored in this collection: { _id: ObjectId(“52cdef7c4bab8bd675297da4”), name: ‘Powerset’, category_code: ‘search’, founded_year: 2006 }, { _id: ObjectId(“52cdef7c4bab8bd675297da5”), name: ‘Technorati’, category_code: ‘advertising’, founded_year: 2002 }, { _id: ObjectId(“52cdef7c4bab8bd675297da7”), name: ‘AddThis’, category_code: ‘advertising’, founded_year: 2004 }, { _id: ObjectId(“52cdef7c4bab8bd675297da8”), name: ‘OpenX’, category_code: ‘advertising’, founded_year: 2008 }, { _id: ObjectId(“52cdef7c4bab8bd675297daa”), name: ‘Sparter’, category_code: ‘games_video’, founded_year: 2007 }, { _id: ObjectId(“52cdef7c4bab8bd675297dac”), name: ‘Veoh’, category_code: ‘games_video’, founded_year: 2004 }, { _id: ObjectId(“52cdef7c4bab8bd675297dae”), name: ‘Thoof’, category_code: ‘web’, founded_year: 2006 } How many documents will be returned in response to the following aggregation pipeline? [{ $group: { _id: ‘$category_code’, number_of_companies: { $sum: 1 } }}, { $sort: { number_of_companies: -1 }}, { $limit: 3 }]

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QUESTION 95
Given a companies collection where each document has the following structure:
{ _id: ObjectId(’61a8b90c6d5ce6a7d8fef95e’), name: ‘Facebook’, tag_list: [‘facebook’, ‘college’, ‘students’, ‘network’], description: ‘Social network’ }
Which of the following commands will add new fields to the updated documents?

db.companies.updateMany({ “name”: “Facebook” }, { “$push”: { “tag_list”: “media” } })

db.companies.updateMany({ “name”: “Facebook” }, { “$set”: { “description”: “Social media” } })

db.companies.updateMany({ “name”: “Facebook” }, { “$set”: { “country”: “USA” } })

QUESTION 96
What command can you use to create a capped collection named latest_news that will be limited to 3 documents and 10,000 bytes?

db.createCollection(‘latest_news’, {‘capped’: true, ‘size’: 10000, ‘max’: 3})

db.createCollection(‘latest_news’, {‘capped’: true, ‘max’: 3})

db.createCollection(‘latest_news’, {‘size’: 10000, ‘max’: 3})

QUESTION 97
What can you deduce from the explain() method?
For example:
db.collection.find().explain()

All stages that the query must go through with details about the time it takes, number of documents processed and returned to the next stage in the pipeline.

All available indexes for this collection.

The index used by the chosen plan.

Whether the sort stage was performed by index or performed in memory.

QUESTION 98
Use case: e-learning platform Which of the following scenarios is the best candidate to use the Subset Pattern?

Our app needs to retrieve a course and its ten most recent reviews.

Our app needs to retrieve a course and information about its instructor.

A course model needs to store references to image of the course that are kept in an external location outside the database.

A course model needs to store a counter representing the number of times it was purchased.

QUESTION 99
Which of the following commands are valid to start a mongod?

mongod –dbpath /data/db –fork

mongod -f /etc/mongod.conf

mongod –logpath /var/log/mongo/mongod.log –dbpath /data/db –fork

mongod –log /var/log/mongo/mongod.log –db /data/db –fork

QUESTION 100
Select all true statements about MongoDB documents.

MongoDB documents must have the same fields in the collection.

MongoDB documents are stored as BSON documents.

MongoDB documents have a flexible schema.

MongoDB documents are stored as JSON documents.

QUESTION 101
What is the built-in database called admin in MongoDB for?

The admin database is used to store information about shards in shared MongoDB cluster.

The admin database stores data describing the MongoDB server. For replica sets, it also stores information about the replication process.

The admin database plays an important role in the authentication and authorization process. Certain actions performed by administrators also require access to this database.

QUESTION 102
Suppose you added the following index to a products collection: { product_category: 1 } Which of the following operations can potentially decrease performance?

db.products.insertOne( { product_category: ‘clothes’ } )

db.products.find( { product_category: ‘clothes’ } )

db.products.updateOne( { product_category: ‘shoes’ }, { $set: company: ‘Nike’ } )

QUESTION 103
What is the best practice in using the $match operator?

The later in the pipeline, the better.

The earlier in the pipeline, the better. Not only because we will be using expression filters which reduce the number of documents to be processed, but also because we can use indexes.

It doesn’t matter when we apply $match stage.

QUESTION 104
Which collection method do you need to use to drop a specific collection?

db.collection.drop()

db.collection.dropIndex()

db.collection.dropCollection()

db.collection.remove()

QUESTION 105
We have a movies collection with the following document structure: { _id: ObjectId(“573a1390f29313caabcd6223”), genres: [ ‘Comedy’, ‘Drama’, ‘Family’ ], title: ‘The Poor Little Rich Girl’, released: ISODate(“1917-03-05T00:00:00.000Z”), year: 1917, imdb: { rating: 6.9, votes: 884, id: 8443 } } We need to extract all movies from this collection where genres includes both ‘Crime’ and ‘Mystery’. Which query should we use?

db.movies.find( { genres: { $any: [“Crime”, “Mystery”] } } )

db.movies.find( { genres: { $all: [“Crime”, “Mystery”] } } )

db.movies.find( { genres: { $nin: [“Crime”, “Mystery”] } } )

db.movies.find( { genres: { $in: [“Crime”, “Mystery”] } } )

QUESTION 106
Why adding indexes may lead to slower write operations?

Because we also need to update the index.

Because we have less and less disk space.

QUESTION 107
Suppose you have a mobile_games collection with the following document structure: { game: “Fishing Clash”, company: “Ten Square Games”, platforms: [‘Android’, ‘IOS’], … release_USA: ISODate(“2017-04-09T01:00:00+01:00”), release_France: ISODate(“2017-04-09T01:00:00+01:00”), release_Italy: ISODate(“2017-08-17T01:00:00+01:00”), … } Are there any problems with this document structure?

Yes, a search for a release date will require looking across many fields at once which is inefficient.

No, everything is correct. There is no room for improvement.

QUESTION 108
We have a movies collection with the following document structure: { _id: ObjectId(“573a1390f29313caabcd6223”), genres: [ ‘Comedy’, ‘Drama’, ‘Family’ ], title: ‘The Poor Little Rich Girl’, released: ISODate(“1917-03-05T00:00:00.000Z”), year: 1917, imdb: { rating: 6.9, votes: 884, id: 8443 } } We need to use Aggregation Framework to fetch all movies from this collection where ‘Drama’ is not in genres list and the minimum ‘imdb.votes’ is at least 100. Additionally, in the projection stage, we want to leave only the following fields: -> title -> genres -> imdb.votes We also want to sort the result set by decreasing imdb votes and limit the number of documents retuned to 5. Example output: [ { imdb: { votes: 1294646 }, genres: [ ‘Action’, ‘Mystery’, ‘Sci-Fi’ ], title: ‘Inception’ }, { imdb: { votes: 1109724 }, genres: [ ‘Adventure’, ‘Fantasy’ ], title: ‘The Lord of the Rings: The Fellowship of the Ring’ }, { imdb: { votes: 1081144 }, genres: [ ‘Adventure’, ‘Fantasy’ ], title: ‘The Lord of the Rings: The Return of the King’ }, { imdb: { votes: 1080566 }, genres: [ ‘Action’, ‘Sci-Fi’ ], title: ‘The Matrix’ }, { imdb: { votes: 1004805 }, genres: [ ‘Action’, ‘Thriller’ ], title: ‘The Dark Knight Rises’ } ] Which pipeline should you use?

[{ $match: { genres: { $nin: [‘Drama’] }, ‘imdb.votes’: { $gte: 100 } } }, { $project: { _id: 0, title: 1, genres: 1, ‘imdb.votes’: 1 } }, { $sort: { ‘imdb.votes’: -1 } }, { $limit: 5 }]

[{ $match: { genres: { $in: [‘Drama’] }, ‘imdb.votes’: { $gte: 100 } } }, { $project: { _id: 0, title: 1, genres: 1, ‘imdb.votes’: 1 } }, { $sort: { ‘imdb.votes’: -1 } }, { $limit: 5 }]

[{ $match: { genres: { $nin: [‘Drama’] }, ‘imdb.votes’: { $gte: 100 } } }, { $project: { _id: 0, title: 1, genres: 1, ‘imdb.votes’: 1 } }, { $sort: { ‘imdb.votes’: -1 } }]

QUESTION 109
Select all true statements about data modeling in MongoDB.

MongoDB can easily handle both unstructured and structured data sets.

Unlike SQL databases, where the table schema must be specified and declared before inserting the data, MongoDB collections don’t, by default, require documents to have the same schema.

The field set and data type for each field can differ across documents within a collection.

In MongoDB we can enforce document validation rules for a collection during update and insert operations.

QUESTION 110
Select all true statements about reconfiguring a replica set with rs.reconfig().

When we reconfigure a replica set with rs.reconfig(), we don’t need to restart any of the individual nodes.

When we reconfigure a replica set with rs.reconfig(), we need to update all of the nodes’ configuration files.

QUESTION 111
Data modeling. You are considering the use of nesting or references in your data model. Documents can grow rapidly. Which option would be more appropriate?

Use of nesting.

Use of reference.