Hi Hans, Thanks for reply. If I set the "view expression" as "SELECT * FROM topic_name" It will read values of all the fields in the topic. But I want to read the values of few selected fields only. In my previous mail I had mentioned that if I set the viewExpression as "SELECT userid, description FROM topicName" , even then it is reading values of all the fields in the topic. Can you please give an example for usage of the view expression to read only selected fields ?
On Thu, Jun 28, 2012 at 4:46 PM, Hans van't Hag
<hans.vant...@prismtech.com>wrote:
> Hi John,
>
>
>
> Here’s a code-snippet that shows how to create a dataReader:
>
>
>
>
>
> /* Create a Subscriber with the QoS provided. */
>
> Subscriber subscriber = participant.createSubscriber("Subscriber",
> sqos);
>
>
>
> /* If no ReaderQoS is provided, copy the QoS of the Topic that
> we're
>
> * about to monitor.
>
> */
>
> if(rqos == null){
>
> rqos =
> ReaderQoS.copyFromTopicQoS((TopicQoS)(topics[0].getQoS()));
>
> }
>
>
>
> /* Create a DataReader for the Topic with the QoS provided.
> Parameters:
>
> * 1. Name of the DataReader
>
> * 2. *The 'view expression' to subscribe to the right topic.
> This must*
>
> * * be 'select * from <topicName>' to get all data for a
> topic. A*
>
> * * where clause can be added to apply a content filter.*
>
> * 3. The QoS to use for the DataReader.
>
> */
>
> DataReader reader = subscriber.createDataReader(
>
> realName + "DataReader",
>
> "select * from " + realName,
>
> rqos);
>
>
>
> Please note that the C&M API rather than being a standardized API is an
> internal API used primarily by our own tools.
>
>
>
> Regards,
>
> Hans
>
>
>
>
>
> * *
>
> *Hans van 't Hag*
>
> OpenSplice DDS Product Manager
>
> PrismTech Netherlands
>
> Email: hans.vant...@prismtech.com
>
> Tel: +31742472572
>
> Fax: +31742472571
>
> Gsm: +31624654078
>
>
>
> PrismTech is a global leader in standards-based, performance-critical
> middleware. Our products enable our OEM, Systems Integrator, and End User
> customers to build and optimize high-performance systems primarily for
> Mil/Aero, Communications, Industrial, and Financial Markets.
> ------------------------------
>
> *From:* developer-boun...@opensplice.org [mailto:
> developer-boun...@opensplice.org] *On Behalf Of *Cristy John
> *Sent:* Thursday, June 28, 2012 6:31 AM
> *To:* developer@opensplice.org
> *Subject:* [OSPL-Dev] datareader view expression
>
>
>
> Hi all,
>
>
>
> I am working on the Control and Monitoring API shipped with Opensplice
> Community Edition V5.5.1
>
>
>
> While creating a org.opensplice.cm.DataReader, we pass three arguments name,
> view, Qos. I am not certain what is the "view". The javadoc says view is "
> *The View that determines what data the DataReader reads" *
>
>
>
> What I am trying to achieve is, to filter the fields of a topic so that I
> can read values of selected fields only. Suppose my topic consists of
> fields [userid, description, data], I want the datareader to read values
> of only userid and description.
>
>
>
> I understand that the opensplice Java API makes a JNI call to
> jniCreateDataReader() to create the datareader. The documentation in the
> C source files say that this view expression is a OQL expression which is a
> subset of SQL SELECT statement.
>
>
>
> I tried using "SELECT userid, description FROM topicName" as the view
> expression. But the datareader is not filtering the fields but reads values
> of all the three fields.
>
>
>
> Can I achieve what I am trying to do ? Can somebody explain how to use the
> "view expression" to filter the fields while creating a datareader using
> C&M API ?
>
>
>
> Thanks & Regards
>
> John
>
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>
>
--
Thanks & Regards
John
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