In MongoDB, the $toUpper aggregation pipeline operator converts a string to uppercase and returns the result.
In MongoDB, the $toLower aggregation pipeline operator converts a string to lowercase and returns the result.
In MongoDB, you can use the $exists element query operator to match documents that contain a specific field.
You can also use it to match documents that don’t contain a specific field.
You can also use it in conjunction with other operators such $nin to match documents where a given field exists, but it doesn’t contain a specific value.
In MongoDB, the cursor.forEach() method iterates the cursor to apply a JavaScript function to each document from the cursor.
In MongoDB, the cursor.map() method applies a function to each document visited by the cursor and combines the return values in an array.
From MongoDB 4.4, you can use the $isNumber aggregation pipeline operator to check whether or not a value is a number.
It accepts any valid expression, and returns true if the expression is a number, false if it’s not.
The $replaceAll aggregation pipeline operator was introduced in MongoDB 4.4.
This operator replaces all instances of a search string in an input string with a replacement string and returns the result.
If the search string isn’t found, then $replaceAll returns the input string.
The $replaceOne aggregation pipeline operator was introduced in MongoDB 4.4.
This operator replaces the first instance of a search string in an input string with a replacement string and returns the result.
If the search string isn’t found, then $replaceOne returns the input string.
MongoDB 4.4 introduced the $last aggregation pipeline operator.
This operator returns the last element in an array.