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Subject: Re: dataAccess V4 Ca client propertyId questions
From: Marty Kraimer <[email protected]>
To: EPICS Core Talk <[email protected]>
Date: Wed, 29 Jun 2005 08:55:13 -0500

On Jun 27, 2005, at 2:03 PM, Kay-Uwe Kasemir wrote:

On Jun 27, 2005, at 12:02, Marty Kraimer wrote:
Can it ask for a list of properrtyIds?
...
Given a list of propertyIds how does it obtain the information associated with each id?
The V4 "client user interface" suggests these in the "DataAccess" interface:
 	 list<string> getProperties()       Get a list of all the properties
 	 type_info getType(string property)
 	 string getAsString(string property)

Ca accepts a request to get data associated with a propertyId. Instead of putting it into a caller provided container via the caller supplied propertyCatalog, CA would make the data available via the caller supplied dataViewer.
We pretend that the CA client library & data access doesn't hold the data,
but only presents an interface for the user to copy the data into a
user-provided container.
Well, while you use dataAccess, the CA client library actually holds
the data in some temporary network buffer.
So you don't need a container at all if you only want to get a list
of all the properties & types.

 Does the proposed CA V4 interface allow this?
Yes, Jeff proposes a channel::createAllPropertiesReadRequest.
Does that cover your idea for a simply 'probe'- type application?

     createAllPropertiesReadRequest
     ...
     foreach p ( da->getProperties() )
     {
         display da->getType(p), da->getAsString(p)
     }

... or would you also like to see a request that only
gets the properties and types, without fetching any actual values?

-Kay

In the above type_info is mentioned.
What is it?
It says that it is part of dataAccess not just part of CA.

But

On Jun 28, 2005, at 8:28 AM, Ralph Lange wrote:
I don't understand. The main feature of dataAccess *is* an introspection interface. Always has been. From day one for the last five years. The traverse() methods have been there for ages. So: By supporting dataAccess I am supporting an introspection interface. Of course.




This does not seem to imply that a type_info is how introspection is supported. I take it to mean that the following is done when a CA client introspects

CA provides a propertyCatalog.
The client implements a propertyViewer which has all the overloaded reveal methods. By seeing which overloadsed method is called it can determine what type associated with the propertyId.


I am confused.

Marty


Replies:
Re: dataAccess V4 Ca client propertyId questions Ralph Lange
References:
dataAccess V4 Ca client propertyId questions Marty Kraimer
Re: dataAccess V4 Ca client propertyId questions Kay-Uwe Kasemir

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