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<p>Hi,</p>
<p>An expression `attribute = 'major_road' AND $id IN (1,2,3)`
should have the same result on the number of features in the
iterator. Or I am missing something.<br>
</p>
<p>Matthias<br>
</p>
<div class="moz-cite-prefix">On 4/30/19 12:13 PM, Alexis R.L. wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAOM0XWCSgeSy4=L5yXRxD-4h8cE6sEnyBpxN40UZOMDoKJtL3Q@mail.gmail.com">
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<div dir="ltr">Greetings Mr.Kuhn,
<div><br>
</div>
<div>Well in my case the fact that each symbol node is evaluated
add some lenght to the computation, if I can make something
that would only iterate over a given list of Fids, (and at the
same time prevent having to iterate over each feature to check
if that feature is within the given list of feature) we would
move from something that takes x by n loops to something that
would only take around x loop ( where x is the number of
features and n is the number of symbol).</div>
<div><br>
</div>
<div>For other use case the gain might be minimal. Other similar
behaviour could be used with selected features (though I'm not
sure if this is a perfect match for this also.) </div>
<div><br>
</div>
<div>This gain in efficiency is why I want to alter the iterator
itself rather than fiddling with expressions, despite the fact
that this is also a possibility but far less optimal for the
reason mentioned above.</div>
<div><br>
</div>
<div>I just want to know what would be the best way to alter the
iteration process without breaking and in a way that could be
leveraged.</div>
<div><br>
</div>
<div>Thanks.</div>
<div><br>
</div>
<div>
<div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">Alexis Roy-Lizotte</div>
</div>
</div>
<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Le mar. 30 avr. 2019 à 02:31,
Matthias Kuhn <<a href="mailto:matthias@opengis.ch"
moz-do-not-send="true">matthias@opengis.ch</a>> a écrit :<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p>Hi,</p>
<p>I like the idea of a nicer API to combine several filter
conditions. Currently the only possibility to perform this
operation is to write a filter expression as a string or
by combining expression nodes.</p>
<p>I am not convinced however that this should be done
directly on QgsFilterRequest level. It feels a bit like
reimplementing the expression engine on another level
again.</p>
<p>Some questions that come to my mind:</p>
<p> * Are these filters always combined with AND or also OR?</p>
<p> * Can these filters eventually be nested?<br>
</p>
<p> * How should we deal with compiling expressions, should
that be implemented again?</p>
<p>An alternative approach would be to work on a nicer API
for an expression builder to require 1) less string
manipulation when building an expression and 2) have more
introspection capabilities when manipulating an
expression.</p>
<p>Regards</p>
<p>Matthias<br>
</p>
<div class="gmail-m_-619512251185950833moz-cite-prefix">On
4/29/19 9:02 PM, Alexis R.L. wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Greetings Mr. Dawson,
<div><br>
</div>
<div>Thanks for the reply,</div>
<div><br>
</div>
<div>The tests that I did with the method in my PR was
provider agnostic but still entailed looping over
every feature to do the check. Could you provide idea
or methods that could enable this behaviour in an API
friendly way?</div>
<div><br>
</div>
<div>Should I make a new iterator entirely or should I
modify existing methods and add a trigger like I
tested in my PR?</div>
<div><br>
</div>
<div>Thanks!<br clear="all">
<div>
<div dir="ltr"
class="gmail-m_-619512251185950833gmail_signature">
<div dir="ltr">Alexis Roy-Lizotte</div>
</div>
</div>
<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Le dim. 28 avr. 2019
à 19:46, Nyall Dawson <<a
href="mailto:nyall.dawson@gmail.com" target="_blank"
moz-do-not-send="true">nyall.dawson@gmail.com</a>>
a écrit :<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">On Sun, 28 Apr 2019
at 07:18, Alexis R.L. <<a
href="mailto:alroyliz0@gmail.com" target="_blank"
moz-do-not-send="true">alroyliz0@gmail.com</a>>
wrote:<br>
><br>
> Greetings Everyone,<br>
><br>
> While working on my PR (9648) I noticed that
expression filter and a list of feature IDs are both
considered the same thing cannot be used as two
filtering criteria.<br>
><br>
> I am aware that the intent was to only have one
element active to filter out features other than the
rectangle(? might be wrong on that one).<br>
><br>
> What I am wondering if it would be a good thing
to have both co exist (mostly for my PR as of now). A
simply way to do so would be to use the give feature
ids as the list to iterate over and check for the
expression if there is one.<br>
<br>
I also think this would be desirable. The tricky part
(well, one<br>
tricky part -- feature iterators are low level stuff,
lots of<br>
complexity there!) is avoiding any API breakage while
adding new<br>
methods to handle your use case.<br>
<br>
The other (SUPER) tricky bit is that any change to
feature requests<br>
usually requires accompanying changes to every vector
data provider in<br>
order to keep consistent behaviour across all these
providers. The<br>
same request should always give the same result,
regardless of the<br>
actual underlying data provider. The consequence of
this is that<br>
you'll need to be update the postgres, mssql, oracle,
OGR, memory,<br>
spatialite, wfs, arcgis feature server, db2, and
vector layer feature<br>
iterator code. You'll also need to add many new unit
tests to cover<br>
all the changes to the different providers.<br>
<br>
Definitely not a trivial change! Don't let this put
you off making it,<br>
but just be aware that this change would take even a
QGIS core<br>
developer a week or more of work to implement.<br>
<br>
Nyall<br>
<br>
<br>
<br>
><br>
> I assume that such a thing might be implemented
without touching the current behaviour, otherwise one
would have to remove either the expression or the IDs
in some case when we want to override the current
filtering method.<br>
><br>
> Using multiple filtering method might be better
than only forcing one and would provide more
flexibility.<br>
><br>
> As I have a PR that is related to this (<a
href="https://github.com/qgis/QGIS/pull/9816"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://github.com/qgis/QGIS/pull/9816</a>
) I would like to address this point in it and would
like to have the discussion occur there as to the best
way to implement such a thing without any breakage if
people are not opposed to having only one filtering
method in qgsfeaturerequest.<br>
><br>
> Thanks and have a nice day!<br>
><br>
> Alex<br>
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