stringAggregationOperators.js

/*String Aggregation Operators

$concat
Concatenates any number of strings.

$split
Splits a string into substrings based on a delimiter. Returns an array of substrings.

$toLower
Converts a string to lowercase.

$toUpper
Converts a string to uppercase

$subsrtBytes
Returns the substring of a string

$indexOffBytes
Searches a string for an occurrence of a substring and returns the UTF-8 byte index of the first
occurrence

$indexOfCP
Searches a string for an occurrence of a substring and returns the UTF-8 code point index of the first occurrence.

$strcasecmp
Performs case-Insensitive string comparison and returns: 0 if two strings are equivalent

$strLenBytes
Returns the number of UTF-8 encoded bytes in a string.$concat.

$strLenCP
Returns the number of UTF-8 code points in a string.

$substrCP
Returns the substring of a string. Starts with the character at the specified LITF-8 code point (CP).

*/

db.products.aggregate([
  {
    $match: { remark: "NEW" },
  },
  {
    $addFields: { newPrice: { $concat: ["$category", " ", "$subcategory"] } },
  },
]);