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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 - A collection and a document in MongoDB is equivalent to which of the SQL concepts respectively?
Answer : A
Explanation
The way SQL databases stores data rows in a table, MonngoDB stores documents inside collections.
Q 2 - Which of the following is true about sharding?
A - Sharding is enabled at the database level
B - Creating a sharded key automatically creates an index on the collection using that key
C - We cannot change a shard key directly/automatically once it is set up
Answer : C
Explanation
There is no direct way of changing the sharded key unless you dump the entire data, drop the sharded key and then re-import everything. Other all options are false. Sharding is enabled at collection level, it does not create any index by default and finally sharding environment supports regular sorting.
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
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 $and operator.
Q 4 - What does the following query do when performed on the posts collection?
db.posts.update({_id:1},{$set:{Author:”Tom"}})
B - Adds a new field Author in the searched collection if not already present
C - Updates only the Author field of the document with _id as 1
Answer : D
Explanation
$set sets the specific fields in the matched documents or adds them as a new field if not already present.
Q 5 - You can implement a multi-document transaction in MongoDB using which of the following concept?
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 is the correct order (lowest to highest) in which MongoDB compares the BSON types?
A - Null, Number, String and Object
B - Number, Null, String and Object
Answer : A
Explanation
This is the defined order in which the bson types are compared. There are various other fields as per the BSON specification which can be found here: http://docs.mongodb.org/manual/reference/bson-types/
Q 7 - In a sharded replica set environment, the w Option provides ability for write concern and j Option provides ability for the data to be written on disk journal. Consider that we have a seven member replica set and we want to assure that the writes are committed to journal. What should be the value of j?
Answer : B
Explanation
To enable the disk journaling commits, j value should always be set to 1.
Q 8 - Which of the following aggregate commands in MongoDB uses a pipeline approach with the goals of improving the aggregation performance?
Answer : A
Explanation
The aggregate command in MongoDB is designed with specific goals of improving performance and usability for aggregation tasks. It uses a “pipeline” approach where objects are transformed as they pass through a series of pipeline operators such as $group, $match, and $sort.
Q 9 - Which of the following operators can reverse the effects of a double unwind operation?
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 - When should we consider representing a one-to-many relationship in an embedded collection instead of separate collection?
A - When the many is very large
Answer : B
Explanation
If the many is very large, then we should create separate collection, else the document size would go on increasing.
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