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 - Which of the following MongoDB query is equivalent to the following SQL query:
UPDATE users SET status = "C" WHERE age > 25
A
db.users.update(
{ age: { $gt: 25 } },
{ status: "C" })
B
db.users.update(
{ age: { $gt: 25 } },
{ $set: { status: "C" } })
C
db.users.update(
{ age: { $gt: 25 } },
{ $set: { status: "C" } },
{ multi: true })
D
db.users.update(
{ age: { $gt: 25 } },
{ status: "C" },
{ multi: true })
Answer : C
Explanation
$set is used to set the value of a particular field in a document. The syntax of set is $set:{column_name : column_value}. Also, {multi:true} is needed to update all the documents. Otherwise only the first found document is updated.
Q 2 - Which of the following command can be used in mongo shell to show all the databases in your MongoDB instance?
Answer : A
Explanation
show dbs returns the list of all the databases.
Q 3 - In our posts collection, which command can be used to find all the posts whose author names begin lie between “A” and “C” in dictionary order?
A - db.posts.find( { post_author : { $gte : "A" , $lte : "C" } } );
B - db.posts.find( { post_author : { $gte : "C" , $lte : "A" } } );
C - db.posts.find( { post_author : { $gt : "A" , $lt : "C" } } );
Answer : A
Explanation
The $gt, $lt and related operators can be applied for string manipulations too. They work in the same manner as they would work on numeric values.
Q 4 - What is the output of following two commands in MongoDB:
db.posts.insert({"_id":1})
db.posts.insert({"_id":1})
A - Two documents will be inserted with _id as 1
B - MongoDB will automatically increment the _id of the second document as 2
C - This will throw a duplicate key error
D - It will insert two documents and throw a warning to the user
Answer : C
Explanation
You cannot insert two documents with the same _id field. The value of _id field should be unique.
Q 5 - Which type of indexes does MongoDB support?
Answer : D
Explanation
MongoDB supports all of the above mentioned indexes.
Q 6 - As per the aggregation pipeline optimization concepts, if you have a $sort followed by a $match:
C - MongoDB does not do any movements by default and will use the order provided
D - Providing these parameters in any order does not impact the performance
Answer : A
Explanation
When you have a sequence with $sort followed by a $match, the $match moves before the $sort to minimize the number of objects to sort.
Q 7 - The following aggregation option is used to specify the specific fields that needs to be passed to the next stage of the aggregation pipeline:
Answer : B
Explanation
The $project operator passes along the documents with only the specified fields to the next stage in the pipeline. The specified fields can be existing fields from the input documents or newly computed fields.
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 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 - The ________ operator limits the contents of an array field from the query results to contain only the first element matching the query condition.
Answer : B
Explanation
The $elemMatch operator limits the contents of an array field from the query results to contain only the first element matching the $elemMatch condition.
