MongoDB Primer

What kind of NoSQL database MongoDB is?

• Document Oriented

• Key Value

• Graph

• Column Oriented

Which of the following is a valid MongoDB JSON document:

• {}

• { "user_id"=1, "user_name"="Joe Sanders", "occupation"=["engineer","writer"] }

• { "user_id":1; "user_name":"Joe Sanders"; "occupation":["engineer","writer"] }

• { "user_id":1, "user_name":"Joe Sanders", "occupation":[ "occupation1":"engineer", "occupation2":"writer" ] }

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

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

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

• Number of posts by an author

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

• Sum of likes on all the posts by all the authors

Consider that you have the following two documents in the products collection:

{ "_id" : 1, "prices" : [ 60, 100, 200 ] }

{ "_id" : 2, "prices" : [ 20, 90, 150 ] }

What will the following query result into:

db.products.update( { _id: 1, prices: 100 }, { $set: { "prices.$" : 111 } } )

• Updates 60 to 100

• Updates 100 to 111

• Updates 60,100 and 200 to 111

• Removes the three elements of the prices array and replaces it only a single element 111

Which of the following aggregation query will sort the posts collection with author key ascending:

• db.posts.aggregate([ {$sort:{ author:1 } } ])

• db.posts.aggregate([ {$sort:{ author:-1 } } ])

• db.posts.aggregate([ {author: {$sort: 1} } ])

• You need to first use $group or $project or $match command before $sort in the pipeline

Which of the following commands create an unique index on author field of the posts collection?

• db.posts.createIndex({"author":1 }, {"unique": true});

• db.posts.createIndex({"author": unique });

• db.posts.createIndex({"author": {$unique:1} });

• db.posts.createIndexUnique({"author":1 });

In a collection that contains 100 post documents, what does the following command do?

db.posts.find().skip(5).limit(5)

• Skip and limit nullify each other. Hence returning the first five documents.

• Skips the first five documents and returns the sixth document five times

• Skips the first five documents and returns the next five

• Limits the first five documents and then return them in reverse order

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

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

• db.posts.findOne({post_text:1})

• db.posts.finOne({},{post_text:1})

• db.posts.findOne({},{_id:0, post_text:1})

A collection and a document in MongoDB is equivalent to which of the SQL concepts respectively?

• Table and Row

• Table and Column

• Column and Row

• Database and Table

Which of the following MongoDB query is equivalent to the following SQL query:

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

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

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

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

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