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- Working with Rockmongo
- MongoDB - GridFS
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- Auto-Increment Sequence
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.
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 - Which of the following is the most important consideration while designing the schema for MongoDB?
A - The schema should match the data access and query patterns
B - The schema should be kept in 3NF similar to SQL schemas
C - The schema should focus on creating possible embedded documents
Answer : A
Explanation
The efficiency of a MongoDB database depends on how well the database is designed depending on the application usage. The schema should be designed based on how the data access patterns are.
Q 4 - Which option should be used to update all the documents with the specified condition in the MongoDB query?
A - updateAll instead of update
B - specify {multi : true} as the third parameter of update command
C - specify {all: true} as the third parameter of update command
D - specify {updateAll: true} as the third parameter of update command
Answer : B
Explanation
{multi:true} should be used for this purpose. By default, MongoDB will update only the first document.
Q 5 - Which of the following operator can be used to limit the number of documents in an array field of a document after an update is performed?
Answer : A
Explanation
You can iterate over all the array elements using $each, slice them using $slice and then push them back to the document using $push.
Q 6 - Which of the following collections are used by MongoDB to store GridFS data?
Answer : A
Explanation
GridFS stores files in two collections: chunks stores the binary chunks and files stores the files metadata.
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 as well as acknowledged by at least 3 nodes. What should be the value of w?
Answer : C
Explanation
The value of w determines the writes are committed and acknowledged by some minimum number of nodes which in this case is 3.
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 - If you have created a compound index on (A,B, C) which of the following access pattern will not be able to utilize the index?
Answer : C
Explanation
Since the index itself starts from A, it cannot be utilized it the input query is starting with B.