MongoDB 4.4 introduced the $first aggregation pipeline operator.
This operator returns the first element in an array.
aggregation
MongoDB $arrayElemAt
In MongoDB, the $arrayElemAt aggregation pipeline operator returns the element at the specified array index.
It accepts two arguments;
- The array
- The index of the element you want to retrieve
MongoDB $bsonSize
From MongoDB 4.4, you can use the $bsonSize aggregation pipeline operator to return the size of a given document in bytes.
$bsonSize accepts any valid expression as long as it resolves to either an object or null.
MongoDB $binarySize
From MongoDB 4.4, you can use the $binarySize aggregation pipeline operator to return the size of a given string or binary data value’s content in bytes.
It accepts any valid expression as long as it resolves to either a string or binary data value. The argument can also be null, in which case, $binarySize returns null.
MongoDB $type Aggregation Pipeline Operator
In MongoDB, the $type aggregation pipeline operator returns the BSON type of its argument.
You can use it to find out the type of a given field.
MongoDB $toObjectId
From MongoDB 4.0, you can use the $toObjectId aggregation pipeline operator to convert a string to an ObjectId.
The string must be a hexadecimal string of length 24.
MongoDB $rtrim
In MongoDB, the $rtrim aggregation pipeline operator removes whitespace from the end of a string. This includes the null character.
It can also remove any character specified. For example, you could use it to remove all periods (.), exclamation marks (!), etc from the end of a string.
MongoDB $ltrim
In MongoDB, the $ltrim aggregation pipeline operator removes whitespace from the beginning of a string. This includes the null character.
It can also remove any character specified. For example, you could use it to remove all hyphen characters (-) from the beginning of a string.
MongoDB $trim
In MongoDB, the $trim aggregation pipeline operator removes whitespace from the beginning and end of a string. This includes the null character.
It can also remove any character specified. For example, you could use it to remove all hyphen characters (-) or periods (.) or all s characters, etc.
MongoDB Whitespace Characters
The following table contains a list of whitespace characters that MongoDB removes by default when using the $trim, $ltrim, and $rtrim aggregation pipeline operators.