DDS::MultiTopic Class Reference

[Not supported (optional)] <<interface>> A specialization of ::DDS::TopicDescription that allows subscriptions that combine/filter/rearrange data coming from several topics. More...

#include <managed_topic.h>

Inheritance diagram for DDS::MultiTopic:

Public Member Functions
System::String^	get_subscription_expression ()
	Get the expression for this DDS::MultiTopic.
void	get_expression_parameters (StringSeq^ parameters)
	Get the expression parameters.
void	set_expression_parameters (StringSeq^ parameters)
	Set the expression_parameters.
Public Member Functions inherited from DDS::ITopicDescription
System::String^	get_type_name ()
	Get the associated type_name.
System::String^	get_name ()
	Get the name used to create this ::DDS::TopicDescription .
DomainParticipant^	get_participant ()
	Get the DDS::DomainParticipant to which the ::DDS::TopicDescription belongs.

Static Public Member Functions
static MultiTopic^	narrow (ITopicDescription^ topic_description)
	Narrow the given ::DDS::TopicDescription pointer to a DDS::MultiTopic pointer.

Detailed Description

[Not supported (optional)] <<interface>> A specialization of ::DDS::TopicDescription that allows subscriptions that combine/filter/rearrange data coming from several topics.

DDS::MultiTopic allows a more sophisticated subscription that can select and combine data received from multiple topics into a single resulting type (specified by the inherited type_name). The data will then be filtered (selection) and possibly re-arranged (aggregation/projection) according to a subscription_expression with parameters expression_parameters.

• The subscription_expression is a string that identifies the selection and re-arrangement of data from the associated topics. It is similar to an SQL statement where the SELECT part provides the fields to be kept, the FROM part provides the names of the topics that are searched for those fields, and the WHERE clause gives the content filter. The Topics combined may have different types but they are restricted in that the type of the fields used for the NATURAL JOIN operation must be the same.

• The expression_parameters attribute is a sequence of strings that give values to the 'parameters' (i.e. "%n" tokens) in the subscription_expression. The number of supplied parameters must fit with the requested values in the subscription_expression (i.e. the number of n tokens).

• DDS::DataReader entities associated with a DDS::MultiTopic are alerted of data modifications by the usual DDS::Listener or DDS::WaitSet / DDS::Condition mechanisms whenever modifications occur to the data associated with any of the topics relevant to the DDS::MultiTopic.

Note that the source for data may not be restricted to a single topic.

DDS::DataReader entities associated with a DDS::MultiTopic may access instances that are "constructed" at the DDS::DataReader side from the instances written by multiple DDS::DataWriter entities. The DDS::MultiTopic access instance will begin to exist as soon as all the constituting DDS::Topic instances are in existence. The view_state and instance_state is computed from the corresponding states of the constituting instances:

• The view_state of the DDS::MultiTopic instance is DDS::ViewStateKind::NEW_VIEW_STATE if at least one of the constituting instances has view_state = DDS::ViewStateKind::NEW_VIEW_STATE. Otherwise, it will be DDS::ViewStateKind::NOT_NEW_VIEW_STATE.

• The instance_state of the DDS::MultiTopic instance is DDS::InstanceStateKind::ALIVE_INSTANCE_STATE if the instance_state of all the constituting DDS::Topic instances is DDS::InstanceStateKind::ALIVE_INSTANCE_STATE. It is DDS::InstanceStateKind::NOT_ALIVE_DISPOSED_INSTANCE_STATE if at least one of the constituting DDS::Topic instances is DDS::InstanceStateKind::NOT_ALIVE_DISPOSED_INSTANCE_STATE. Otherwise, it is DDS::InstanceStateKind::NOT_ALIVE_NO_WRITERS_INSTANCE_STATE.

Queries and Filters Syntax describes the syntax of subscription_expression and expression_parameters.

Member Function Documentation

static MultiTopic ^ DDS::MultiTopic::narrow ( ITopicDescription^  topic_description )

inlinestatic

Narrow the given ::DDS::TopicDescription pointer to a DDS::MultiTopic pointer.

Returns

DDS::MultiTopic if this ::DDS::TopicDescription is a DDS::MultiTopic. Otherwise, return NULL.

System::String ^ DDS::MultiTopic::get_subscription_expression ( )

inline

Get the expression for this DDS::MultiTopic.

The expressions syntax is described in the DDS specification. It is specified when the DDS::MultiTopic is created.

Returns

subscription_expression of the DDS::MultiTopic.

void DDS::MultiTopic::get_expression_parameters ( StringSeq^  parameters )

inline

Get the expression parameters.

The expressions syntax is described in the DDS specification.

The parameters is either specified on the last successful call to DDS::MultiTopic::set_expression_parameters, or if DDS::MultiTopic::set_expression_parameters was never called, the parameters specified when the DDS::MultiTopic was created.

Parameters

parameters

<<inout>> Fill in this sequence with the expression parameters. Cannot be NULL.

Exceptions

One	of the Standard Return Codes

void DDS::MultiTopic::set_expression_parameters ( StringSeq^  parameters )

inline

Set the expression_parameters.

Changes the expression_parameters associated with the DDS::MultiTopic.

Parameters

parameters

<<in>> the filter expression parameters

Returns

One of the Standard Return Codes.