/**
* Append one or more values to the current array field.
*
* If the field does not exist, it will be set to an array containing the
* value(s) in the argument. If the field is not an array, the query
* will yield an error.
*
* Multiple values may be specified by providing an Expr object and using
* {@link Expr::each()}. {@link Expr::slice()} and {@link Expr::sort()} may
* also be used to limit and order array elements, respectively.
*
* @see Expr::push()
* @see http://docs.mongodb.org/manual/reference/operator/push/
* @see http://docs.mongodb.org/manual/reference/operator/each/
* @see http://docs.mongodb.org/manual/reference/operator/slice/
* @see http://docs.mongodb.org/manual/reference/operator/sort/
* @param mixed|Expr $valueOrExpression
* @return self
*/
public function push($valueOrExpression)
{
$this->expr->push($valueOrExpression);
return $this;
}