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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