mongodb更新器

Name    Description
$inc    Increments the value of the field by the specified amount.
$mul    Multiplies the value of the field by the specified amount.
$rename    Renames a field.
$setOnInsert    Sets the value of a field if an update results in an insert of a document. Has no effect on update operations that modify existing documents.
$set    Sets the value of a field in a document.
$unset    Removes the specified field from a document.
$min    Only updates the field if the specified value is less than the existing field value.
$max    Only updates the field if the specified value is greater than the existing field value.
$currentDate    Sets the value of a field to current date, either as a Date or a Timestamp.