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})
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.
Answer : A
Explanation
In the default configuration, MongoDB writes data to the main data files on disk every 60 seconds.
Q 3 - Which of the following commands will return all the posts with number of likes greater than 100 and less than 200, both inclusive?
A - db.posts.find({ likes : { $gt : 100, $lt : 200 } } );
B - db.posts.find({ likes : { $gte : 100, $lt : 200 } } );
C - db.posts.find({ likes : { $gt : 100 , $lte : 200 } } );
D - db.posts.find({ likes : { $gte : 100 , $lte : 200 } } );
Answer : D
Explanation
Since 100 and 200 are both inclusive, we need $gte (greater than and equal) and $lte (less than and equal).
Q 4 - Which option can be used with update command so that a new document gets created if no matching document is found based on the query condition?
A - Specify {upsert : true } as the third parameter of update command
B - upsert command instead of update command
C - {update: true, insert: true} as the third parameter of update command
Answer : A
Explanation
When you specify upsert: true for an update operation and no matching documents are found, MongoDB creates a new document.
Q 5 - If the value of totalKeysExamined is 30000 and the value of totalDocsExamined is 0, which of the following option is correct?
A - The query used an index to fetch the results
B - The query returned 30000 documents after scanning the documents
Answer : A
Explanation
When an index covers a query, the explain result has an IXSCAN stage that is not a descendant of a FETCH stage, and in the executionStats, the totalDocsExamined is 0.
Q 6 - For capped collection, cursors which do not automatically close and remain open after the client exhausts the results are called:
Answer : B
Explanation
By default, MongoDB will automatically close a cursor when the client has exhausted all results in the cursor. However, for capped collections you may use a Tailable Cursor that remains open after the client exhausts the results in the initial cursor.
Answer : B
Explanation
The minimum number of sensible number of voting nodes is 3.
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 is the correct syntax for starting a new mongod process and specifying its replica set name as rs0:
D - First execute this: mongod --replSet. And then execute this: rs.add()
Answer : A
Explanation
Replica set can be set/stated using the –replSet command and specifying the replica name with it.
Q 10 - Which command can be used to rebuild the indexes on a collection in MongoDB?
A - db.collection.createIndex({reIndex:1})
Answer : C
Explanation
If you need to rebuild indexes for a collection you can use the db.collection.reIndex() method to rebuild all indexes on a collection in a single operation. This operation drops all indexes, including the _id index, and then rebuilds all indexes.
