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<== Date ==> <== Thread ==>
Subject: Re: Possible to create aliases for record fields?
From: Andrew Johnson via Tech-talk <tech-talk at aps.anl.gov>
To: "Hu, Yong" <yhu at bnl.gov>, Michael Davidsaver <mdavidsaver at gmail.com>, Zimoch Dirk <dirk.zimoch at psi.ch>
Cc: "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Date: Mon, 2 Jan 2023 21:43:55 -0600
On 1/2/23 3:53 PM, Hu, Yong via Tech-talk wrote:

Michael, we are talking about fields here. So “det1:NELM.RTYP” itself is not valid.

If "det1" is an IOC record, then "det1.RTYP" is definitely a PV name that the IOC will respond to. "RTYP" is a record attribute that the IOC adds to all record types, which returns the name of the record type. Some CA client applications (e.g. MEDM, capr.pl, CS-Studio's pvtree) query that attribute automatically for some/all of the channels they connect to, so a field alias such as the one suggested could result in the IOC seeing requests for that PV name.

Michael's question is thus a valid one. For a simple/naive implementation of this feature the answer might be that the channel name “det1:NELM.RTYP” would time out, and such field aliases just wouldn't support the capr.pl or pvtree applications at all in that case. That might be acceptable, but I would want to be shown that any implementation would not significantly increase the amount of work that the IOC's CA Search thread has to do.

- Andrew


From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>
Date: Monday, January 2, 2023 at 3:37 PM
To: Zimoch Dirk <dirk.zimoch at psi.ch>
Cc: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Possible to create aliases for record fields?

On 12/28/22 03:47, Zimoch Dirk via Tech-talk wrote:
> At the moment, that is not possible. I had planned for quite some time to implement that.

> ... But I don‘t know what the core developers think of this.

Aliasing fields seem like a reasonable feature.  Although it isn't yet clear
to me how this would work in detail.  eg. to take an example from below.

>> alias("det1.NELM", "det1:NELM")

What would "caget det1:NELM.RTYP" return?

There may also be complications depending on what changes to the
'struct dbBase' tree would be needed.



> Dirk
>
>> Am 20.12.2022 um 19:50 schrieb Li, Ji via Tech-talk <tech-talk at aps.anl.gov>:
>>
>> 
>> Hi,
>>
>> I'm trying to access record fields as PVs using alias command, such as:
>>
>> alias("det1.NELM", "det1:NELM")
>> alias("det1.TSEN", "det1:TSEN")
>>
>> The IOC didn't report errors, but apparently they all pointed to det1 as the change to det1 appeared on these aliases, and vice versa, and this was proved by dbla.
>>
>> If alias command is not the right choice, are there any ways to create aliases/dummy PVs for fields?
>>
>> Best,
>> -Ji Li
>>


-- 
Complexity comes for free, Simplicity you have to work for.
Replies:
Re: Possible to create aliases for record fields? Michael Davidsaver via Tech-talk
References:
Re: Possible to create aliases for record fields? Michael Davidsaver via Tech-talk
Re: Possible to create aliases for record fields? Hu, Yong via Tech-talk
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