Name	Description
$comment	Used to add a comment to the query
$explain	Used to report documents with an execution plan
$hint	Used to specify the index for a query
max()	Used to specify the upper limit for the index of a query
min()	Used to specify a lower limit for the index of a query
$maxTimeMS	Used to specify the maximum time for query execution in milliseconds
$orderby	Deprecated, used for sorting documents
$query	Used to specify conditions to request a document
$returnKey	Used to provide the index key from the result
$showDiskLoc	Deprecated, used to show disk location

Examples

1. $comment in MongoDB

$comment is used to add a comment to the query. Comments are not stored in the database. If we want comments to be stored , add the comment as field and value in the document. $comment can be used as follows

Syntax:

db.collection.find( { condition }).comment( add_comment_related_to_condition )
or 
db.collectionj.find(  {  condition } ,$comment : "comment"   )

Example

Add a comment to the document which is not divisible by 3.

Query:

//collection used for example.
 db.Digits.insertMany([{value:1},{value:12},{value:21},{value:27}]);
the db.Digits.find({ value: { $mod: [3, 1] } }).comment("Number not divisible by 3");

Output:

Explanation: find() method is used to request the document with a particular condition and $comment is used to provide details about the query .

2. $explain in MongoDB

$explain is used to report documents with an execution plan.

Syntax:

db.collection.find( { condition } ).explain(" executionStats") ;

Query:

GeeksforGeeks> db.Digits.find({ value: { $mod: [3, 1] } }).explain("executionStats");

Output contains various fields like explainVarsion, ,QueryPlanner,namespace,indexFilterSet and many more.

3. $hint in MongoDB

$hint is used to specify the index for a query. It is deprecated instead of it hint() is used.$text query cannot be used along with the hint() method. Initally indexes are to be created on the collection.createIndex() method is used to create an index.

Syntax:

db.collection.find().hint( { indexKey} ) 

Example: Use hint() in MongoDB

Query:

db.Digits.createIndex( {value:1});
db.Digits.find().hint({ value:1});

Output:

Explanation: Initially indexes are created on the collection using the createIndex() method.In the next query hint() method along with the find() method is used to get the result.

4. min() and max() in MongoDB

min() and max() are used to specify lower and upper limits respectively for the index in a query.

Syntax for min():

db.collection.find(condition).min( { field: lower limit }).hint( {index})

Syntax for max():

db.collection.find({condition}).max( { field: upper limit }).hint( index);

Example: Use min() and max() on Digits collection

Query:

db.Digits.find( { value : {$ gt :10}}  ).min( { value:5}).hint( { value: 1});
db.Digits.find( { value : {$ lt :25}}  ).max( { value:20}).hint( { value: 1});

Output:

Explanation:

• In the first query, Find() method is used to find the document with a value lesser than 25, and the max() method specifies the upper limit of 20 hence the documents below the upper limit that satisfy the condition are returned.
• In the second query, Find() method is used to find the document with value greater than 10 and min() method specify the lower limit to 5 hence the document above the lower limit that satisfy the condition are returned.

5. $maxTimeMS in MongoDB

$maxTimeMS is used to specify the maximum time in which the query should be executed. $maxTimeMS operator is deprecated instead of maxTimeMs() is used. Time is specified in millisecond with integral value and it should be in the range of [0 , 2147483647].

Syntax:

db.collection_name.find().maxTimeMs(mention maximum time);

Example : Use maxTimeMS() method

Query:

db.Digits.find().maxTimeMS(100);

Output:

Explanation: In the above example,Digits collections is used to store the documents.Documents are requested using find() and maxTimeMS() methods. maxTimeMS() is used to specify the maximum time in which the query should be executed.

6. $orderby in MongoDB

$orderby is deprecated, sort() method performs the same operation as $orderby. sort() carries out sorting of the documents in a specific order.Sort direction is specified by 1 and -1.1 for ascending order and -1 for descending.

Syntax:

For ascending order
db.collection_name.find().sort( {field: 1} );
for descending order
db.collection_name.find().sort( { field : -1})

Example: Use sort() method to sort the documents

Query:

db.Digits.find().sort({ values: -1} ) 

Output:

Explanation: The output contains the documents in the descending order.sort() method is used to sort the documents. As field is specified with -1 ,documents are displayed in descending order.

Conclusion

Understanding and utilizing query modifiers in MongoDB can significantly enhance database interactions and application performance. With the shift to cursor methods, MongoDB has made these operations more intuitive and efficient, benefiting developers in writing clearer and more optimized queries.

FAQs on Query Modifiers

What is the purpose of the $comment operator in MongoDB?

The $comment operator is used to add a comment to a query, which can help in identifying and understanding the purpose of the query during debugging or query analysis.

How does the $explain operator benefit query optimization?

The $explain operator provides an execution plan for a query, allowing developers to see how MongoDB executes the query and identify potential performance issues.

When should I use the hint() method in MongoDB?

The hint() method should be used when you want to force MongoDB to use a specific index for a query, which can be useful for optimizing query performance in certain situations.

What is the significance of maxTimeMS() in MongoDB queries?

The maxTimeMS() method sets a maximum execution time for a query in milliseconds. If the query exceeds this time, MongoDB will terminate the operation, helping to manage long-running queries and resource utilization.