$cmp Operator - (MongoDB Miscellaneous)

MongoDB provides a set of operators that can be used to perform various operations. One such operator is the $cmp operator, which compares two values and returns -1, 0 or 1 based on whether the first value is less than, equal to, or greater than the second value. In this page, we will discuss the $cmp operator in MongoDB.

Syntax

{ $cmp: [ <expression1>, <expression2> ] }

Example

Consider a collection named "books" which has the following documents:

{ _id: 1, title: "The Great Gatsby", author: "F. Scott Fitzgerald", price: 10 }
{ _id: 2, title: "To Kill a Mockingbird", author: "Harper Lee", price: 12 }
{ _id: 3, title: "1984", author: "George Orwell", price: 8 }

The following query uses the $cmp operator to compare the price value of each book document with the value 10 and returns books which have a price greater than 10.

db.books.find( { $cmp: [ "$price", 10 ] } : { $gt: 0 } )

The output of the above query would be:

{ _id: 2, title: "To Kill a Mockingbird", author: "Harper Lee", price: 12 }

Explanation

The $cmp operator compares the two expressions specified in the array. If the first expression is less than the second expression, then $cmp returns -1. If the two expressions are equal then $cmp returns 0. If the first expression is greater than the second expression, then $cmp returns 1.

In the example above, we used the $cmp operator to compare the price value of book documents to the value 10. If the price is greater than 10, then $cmp will return 1. We then specified the result of $cmp as the input to the $gt operator. The $gt operator returns true if the expression is greater than the specified value (0 in this case), which indicates that the price value of the book document is greater than 10.

Use

The $cmp operator is used to compare two values in MongoDB. It is particularly useful when used in an aggregation pipeline to compare fields in a document and perform a specific operation based on the comparison result.

Important Points

• The $cmp operator compares two expressions in MongoDB and returns -1, 0, or 1 based on the comparison result.
• It is often used in an aggregation pipeline to compare fields in a document and perform a specific operation based on the comparison result.

Summary

In this page, we discussed the $cmp operator in MongoDB. We covered the syntax, example, output, explanation, use, and important points of the $cmp operator. By using the $cmp operator, you can compare two values in MongoDB and use the comparison result in various operations such as aggregation pipelines.