MultiTopic Class

MultiTopic is an implementation of ITopicDescription that allows subscriptions to combine/filter/rearrange data coming from several topics. 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 the expression parameters.

Inheritance Hierarchy

SystemObject
OpenDDSharp.DDSTopicDescription
OpenDDSharp.DDSMultiTopic

Namespace: OpenDDSharp.DDS
Assembly: OpenDDSharp (in OpenDDSharp.dll) Version: 0.4.1.0

Syntax

C++

Copy

public class MultiTopic : TopicDescription

Public Class MultiTopic
	Inherits TopicDescription

public ref class MultiTopic : public TopicDescription

type MultiTopic =  
    class
        inherit TopicDescription
    end

The MultiTopic type exposes the following members.

Properties

	Name	Description
	Name	Gets the name used to create the ITopicDescription. (Inherited from TopicDescription.)
	Participant	Gets the DomainParticipant to which the ITopicDescription belongs. (Inherited from TopicDescription.)
	SubscriptionExpression	Gets the subscription expression associated with the MultiTopic. That is, the expression specified when the MultiTopic was created.
	TypeName	Gets type name used to create the ITopicDescription. (Inherited from TopicDescription.)

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Methods

	Name	Description
	Equals	Determines whether the specified object is equal to the current object. (Inherited from Object.)
	GetExpressionParameters	Gets the expression parameters associated with the MultiTopic. That is, the parameters specified on the last successful call to SetExpressionParameters(String), or if it was never called, the parameters specified when the MultiTopic was created.
	GetHashCode	Serves as the default hash function. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	SetExpressionParameters	Changes the expression parameters associated with the MultiTopic.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

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 clause 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 are a collection of strings that give values to the ‘parameters’ ("%n" tokens) in the subscription expression. The number of supplied parameters must fit with the requested values in the subscription expression (the number of %n tokens).

DataReader entities associated with a MultiTopic are alerted of data modifications by the usual listener or condition mechanisms whenever modifications occur to the data associated with any of the topics relevant to the MultiTopic.

DataReader entities associated with a MultiTopic access instances that are “constructed” at the DataReader side from the instances written by multiple DataWriter entities.The MultiTopic access instance will begin to exist as soon as all the constituting 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 MultiTopic instance is NewViewState if at least one of the constituting instances has NewViewState, otherwise it will be NotNewViewState.
The instance state of the MultiTopic instance is AliveInstanceState if the instance state of all the constituting Topic instances is AliveInstanceState. It is NotAliveDisposedInstanceState if at least one of the constituting Topic instances is NotAliveDisposedInstanceState. Otherwise it is NotAliveNoWritersInstanceState.

Reference

OpenDDSharp.DDS Namespace