MongoDB $reverseArray Operator
The MongoDB $reverseArray operator is a valuable tool for reversing the order of elements in an array, commonly used for various processing or presentation purposes. In this article, We will learn about the MongoDB $reverseArray Operator by understanding various examples in detail.
MongoDB $reverseArray Operator
- MongoDB $reverseArray Operator is useful when we need to reverse the order of elements in an array for processing or presentation purposes.
- $reverseArray provides a straightforward way to manipulate array data in MongoDB.
- $reverseArray takes an array as an input and returns a new array with the elements in reversed order
- $reverse array operator provides an easy way to change the order of array elements and reverse it.
Syntax:
The syntax of the $reverseArray operator is:
{ $reverseArray: <array expression> }
Here, the given arguments must be a valid expression until it resolves to an array.
Examples of MongoDB $reverseArray
To understand it better, let’s look at some examples of the $reverseArray Operator in MongoDB.
In the following examples, we are working with:
Database: GeeksforGeeks
Collection: arrayExample
Document: three documents that contain the details in the form of field-value pairs.
Output:
Example 1: Using $reverseArray Operator
In this example, we are going to reverse the value of the numbers2 field using $reverseArray operator. Here, the value of the numbers2 field is an array and the elements of the array are numbers.
db.arrayExample.aggregate([
... {$match: {name: "Lolo"}},
... {$project: {
... revNumbers: {$reverseArray: "$numbers2"}}}])
Example 2: Using $reverseArray Operator on Array of Strings
In this example, we are going to reverse the value of the fruits field using $reverseArray operator. Here, the value of the fruits field is an array and the elements of the array are strings(i.e. fruits names).
db.arrayExample.aggregate([
... {$match: {name: "Bongo"}},
... {$project: {
... revStrings: {$reverseArray: "$fruits"}}}])
Example 3: Using $reverseArray Operator in the Embedded Document
In this example, we are going to reverse the value of the favGame.outdoorGames field using $reverseArray operator. Here, the value of the favGame.outdoorGames field is an array and the elements of the array are strings(i.e. outdoor games names).
db.arrayExample.aggregate([
... {$match: {name: "Piku"}},
... {$project: {
... result: {$reverseArray: "$favGame.outdoorGames"}}}])
KeyTakeAways on MongoDB $reverseArray Operator
- The MongoDB $reverseArray operator is used in the aggregation pipeline stages to reverse the order of elements in an array.
- It accepts an array expression as an argument and returns an array with the elements in reverse order.
- If the argument does not resolve to an array or null, then this operator will give an error.
- If the entered argument resolves a null value, then this operator will return null.
- If the entered argument refers to a missing field, then this operator will return null.
- If the entered argument is an empty array, then this operator will return an empty array.
- If the entered argument contains subarrays, then this operator will work on the top-level array elements and will not reverse the contents of subarrays.
Conclusion
The MongoDB $reverseArray operator offers a convenient way to reverse the order of elements in an array, providing flexibility in array manipulation within MongoDB documents. Its straightforward syntax and ability to handle various scenarios make it a valuable tool for developers working with array data in MongoDB.
FAQs on MongoDB $reverseArray
Can the $reverseArray operator reverse the contents of subarrays within an array?
No, the $reverseArray operator works only on the top-level array elements and does not reverse the contents of subarrays.
What happens if the argument to $reverseArray is not an array?
If the argument does not resolve to an array or is null, the $reverseArray operator will return an error.
Can $reverseArray be used in update operations to reverse arrays in documents?
No, $reverseArray is used in the aggregation pipeline and cannot be directly used in update operations to modify documents.
Does the $reverseArray operator modify the original array, or does it return a new array with the elements reversed?
$reverseArray returns a new array with the elements in reverse order, leaving the original array unchanged.
