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<div class="moz-cite-prefix">I remember there was some discussion to
refactor listeners to drop the concept of pre-events and have the
previous value available in the post-event (where applicable). I
do not remember what decision was made about this. But if we do
it, that would be already a big backwards incompatible change, so
modifying some defaults regarding the behavior of the Listener
annotation is just mildly disturbing. We'll have to
apologize/document this anyway and also provide migration advice.<br>
<br>
On 08/22/2016 09:15 PM, William Burns wrote:<br>
</div>
<blockquote
cite="mid:CA+YCuUOW4kRhtvXhefC1Hdmt2i0vzFYh9BKny+JHzPRe6vw_+w@mail.gmail.com"
type="cite">
<div dir="ltr">I like the idea of having a variable to set on the
listener annotation. This way we can know for sure if we need
to force previous values for some listeners and not for others.
<div><span style="line-height:1.5"><br>
</span></div>
<div><span style="line-height:1.5">It seems the default should
be to force the previous value to be more inline with the
current behavior, but I fear no one will use the opposite in
this case though. What do you guys think?</span></div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, Aug 22, 2016 at 4:31 AM Adrian Nistor
<<a moz-do-not-send="true" href="mailto:anistor@redhat.com">anistor@redhat.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Radim,<br>
<br>
Continuous query is built on top of these listeners. CQ
_always_ needs<br>
the previous value and it is very convenient in this case that
the<br>
command is forced to load the previous value. I imagine there
may be<br>
other use cases where we cannot live without the prev value.<br>
<br>
I think the listener should be able to state if it needs the
prev value<br>
at registration time. Maybe add a new attribute in the
Listener<br>
annotation? Similar to how we handled Observation.<br>
<br>
Adrian<br>
<br>
On 08/19/2016 11:34 PM, Radim Vansa wrote:<br>
> Hi,<br>
><br>
> as I am trying to simplify current entry wrapping and
distribution code,<br>
> I often find that listeners can get wrong previous value
in the event,<br>
> and it sometimes forces the command to load the value
even if it is not<br>
> needed for the command.<br>
><br>
> I am wondering if we should change the previous value in
events to<br>
> Optional - we can usually at least detect that we cannot
provide a<br>
> reliable value (e.g. after retry due to topology change,
or because the<br>
> command did not bothered to load the previous value from
cache loader)<br>
> and return empty Optional.<br>
><br>
> WDYT?<br>
><br>
> Radim<br>
><br>
<br>
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