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ContentFilteredTopic

A |ContentFilteredTopic-api| is a specialization of the broader concept of :ref:`dds_layer_topic_topicDescription`. A ContentFilteredTopic is a Topic with filtering properties. It makes it possible to subscribe to a Topic while at the same time specify interest on a subset of the Topic's data.

Important

Note that a ContentFilteredTopic can only be used to create a DataReader, not a DataWriter.

A ContentFilteredTopic provides a relationship between a :ref:`dds_layer_topic_topic`, called the related topic, and some user-defined filtering properties:

  • A filter expression, which establishes a logical expression on the content of the related topic. It is similar to the WHERE clause in a SQL statement.
  • A list of expression parameters, which give values to the parameters present in the filter expression. There must be one parameter string for each parameter in the filter expression.

Note that a ContentFilteredTopic is not an Entity, and thus it has neither QoS nor listener. A DataReader created with a ContentFilteredTopic will use the QoS from the related topic. Multiple DataReaders can be created for the same ContentFilteredTopic, and changing the filter properties of a ContentFilteredTopic will affect all DataReaders using it.

Please refer to :ref:`dds_layer_topic_filtering_data_on_topic` and :ref:`dds_layer_topic_contentFilteredTopic_writer_side` for more information about how to use |ContentFilteredTopic-api|.