/**
* Append one or more values to the current array field only if they do not
* already exist in the array.
*
* If the field does not exist, it will be set to an array containing the
* unique value(s) in the argument. If the field is not an array, the query
* will yield an error.
*
* Multiple values may be specified by provided an Expr object and using
* {@link Expr::each()}.
*
* @see Expr::addToSet()
* @see http://docs.mongodb.org/manual/reference/operator/addToSet/
* @see http://docs.mongodb.org/manual/reference/operator/each/
* @param mixed|Expr $valueOrExpression
* @return self
*/
public function addToSet($valueOrExpression)
{
$this->expr->addToSet($valueOrExpression);
return $this;
}
