<div dir="ltr">Honestly I have no idea đ<br><br>I mean, of course what is happening is QGIS is needing to identify a field from a text string, and it's even possible that with some convoluted chain of escape characters or funky regex the process could correct itself and "just work".<br><br>In all likelihood you could have just stumbled onto some obscure bug in the underlying processing API where the context of that field object get's dropped or orphaned when trying to access it.<br><br>My assumption is that using attribute() just compensates for whatever is going on under the hood by reinstantiating the context behind the field object, or at the very least provides a robust interface for referencing it ÂŻ\_(ă)_/ÂŻ<br><div><br></div><div>I would definitely call it a work around though</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, 23 Aug 2021 at 18:52, Nicolas Cadieux <<a href="mailto:njacadieux.gitlab@gmail.com">njacadieux.gitlab@gmail.com</a>> wrote:<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>
<p>Hi,</p>
<p>if(attribute(to_string( @<span style="font-family:monospace">NamelengthField</span>
)) != "LENGTH2", TRUE, FALSE ) <br>
</p>
<p>("LENGHT2" is an existing field and @<span style="font-family:monospace">NamelengthField</span> was a model
input string.)<br>
</p>
<p>This worked for me!  If you have the time, please explain why I
needed the <u>attribute()</u> function for this to work. I
looked in the documentation and did not find it very clear.</p>
<p>Thanks a million you saved my butt!<br>
</p>
<p>Nicolas<br>
</p>
<p><br>
</p>
<div>On 2021-07-20 5:53 a.m., Charles
Dixon-Paver wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi Nicholas,
<div><br>
</div>
<div>I haven't had time to dig into this extensively or
encountered this particular issue, but I would suggest trying
to "force" the expression to retrieve the correct info
regardless of context using something like this:</div>
<div><br>
</div>
<span style="font-family:monospace">with_variable('Length2',
 to_string(@NamelengthField) || '2',
if(attribute(to_string(@NamelengthField)) !=
attribute(@Length2), TRUE, FALSE))</span><br>
<div><br>
</div>
<div>That's probably an extreme example but hopefully it
illustrates my point. If you want to share a sample dataset/
model I can try to have a look at how to resolve it.</div>
<div><br>
</div>
<div>Regards</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, 20 Jul 2021 at 10:46,
Richard McDonnell <<a href="mailto:richard.mcdonnell@opw.ie" target="_blank">richard.mcdonnell@opw.ie</a>>
wrote:<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 lang="EN-IE">
<div>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Nicolas,</span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">I
have not looked at this in too much detail, but at a
quick glance, could it not be the fact that you should
be using the newly created fields? As in instead of </span><b>@NamelengthField
!= @NamelengthField || '2'</b>,
<span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">should
it not be more like your previous example</span> <b>Length
!= Length2</b><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Â </span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Regards,</span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Â </span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Richard</span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Â </span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Â </span></p>
<table style="font-size:9pt;height:321px;font-family:Arial,sans-serif;width:500px;line-height:15px" cellspacing="0" cellpadding="0">
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ââ</span><br>
<span style="font-family:Arial,sans-serif;font-weight:bold;color:rgb(0,77,68)">Richard
McDonnell MSc GIS, FME Certified Professional</span><br>
<span style="font-family:Arial,sans-serif;color:rgb(0,77,68)"><i>FRM
Data Management</i></span><br>
<br>
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<div style="border-top:none;border-right:none;border-bottom:none;border-left:1.5pt solid blue;padding:0cm 0cm 0cm 4pt">
<div>
<div style="border-right:none;border-bottom:none;border-left:none;border-top:1pt solid rgb(225,225,225);padding:3pt 0cm 0cm">
<p class="MsoNormal"><b><span style="font-size:11pt;font-family:Calibri,sans-serif" lang="EN-US">From:</span></b><span style="font-size:11pt;font-family:Calibri,sans-serif" lang="EN-US"> Qgis-user <<a href="mailto:qgis-user-bounces@lists.osgeo.org" target="_blank">qgis-user-bounces@lists.osgeo.org</a>>
<b>On Behalf Of </b>Nicolas Cadieux<br>
<b>Sent:</b> 20 July 2021 09:27<br>
<b>To:</b> Qgis Users List <<a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</a>><br>
<b>Subject:</b> Re: [Qgis-user] Problem using
Model Inputs variable in an Select by expression
in the model Designer</span></p>
</div>
</div>
<p class="MsoNormal">Â </p>
<p class="MsoNormal">Hi,</p>
<div>
<p class="MsoNormal" style="margin-bottom:12pt">Does
anyone have an idea?</p>
<div>
<p class="MsoNormal">Nicolas Cadieux</p>
<div>
<p class="MsoNormal"><a href="https://gitlab.com/njacadieux" target="_blank">https://gitlab.com/njacadieux</a></p>
</div>
</div>
<div>
<p class="MsoNormal"><br>
<br>
</p>
<blockquote style="margin-top:5pt;margin-bottom:5pt">
<p class="MsoNormal" style="margin-bottom:12pt">Le
8 juill. 2021 Ă 01:17, Nicolas Cadieux <<a href="mailto:njacadieux.gitlab@gmail.com" target="_blank">njacadieux.gitlab@gmail.com</a>>
a écrit :</p>
</blockquote>
</div>
<blockquote style="margin-top:5pt;margin-bottom:5pt">
<div>
<p class="MsoNormal"><span style="font-family:Tahoma,sans-serif">ï»ż</span>
</p>
<p>Hi,</p>
<p>I am creating a model that fixes Network files
before they are used in the QGIS Network
analysis (Shortest path) tools.</p>
<p>This is my work flow:</p>
<ol type="1" start="1">
<li class="MsoNormal">
Create a "Length" field (value) and calculate
$length in the field calculator</li>
<li class="MsoNormal">
Split the Multipart lines into Singlepart
lines</li>
<li class="MsoNormal">
Create a "Length<b>2</b>" field (value) and
calculate $length in the field calculator</li>
<li class="MsoNormal">
Select by expression Length != Length2. This
basically gives me a selection of line that
have been modified by the Multipart to
Singlepart algorithm. (I get 8 results)</li>
</ol>
<p>This works well</p>
<p>The problem is when I create and Input String
to let the user create a "Length" field. This
become a variable called @NamelengthField. My
work flow become:</p>
<ol type="1" start="1">
<li class="MsoNormal">
User input "Length" in the Model input.
(@NamelengthField)</li>
<li class="MsoNormal">
Create a "Length" field usingÂ
@NamelengthField (as pre-calculated value) and
calculate $length in the field calculator:
This is OK</li>
<li class="MsoNormal">
Split the Multipart lines into Singlepart
lines: This is OK</li>
<li class="MsoNormal">
Create a "Length2" field usingÂ
@NamelengthField ||'2'Â (as pre-calculated
value) and calculate $length in the field
calculator: This is OK this field (Length2) is
created and calculated properly.
</li>
<li class="MsoNormal">
I get stuck when I try Select by expression
using @NamelengthField != @NamelengthField ||
'2' (as pre-calculated value) (I get all lines
back) and the test does not work.</li>
</ol>
<p>I tried stuff like</p>
<p>@NamelengthField != (@NamelengthField || '2')</p>
<p>'@NamelengthField != @NamelengthField || '2''</p>
<p>"@NamelengthField != @NamelengthField || '2'"</p>
<p>"@NamelengthField"|| !=|| "@NamelengthField ||
'2'"</p>
<p>Even simple @NamelengthField =
5.286365157529550 (which should extract exactly
one value).Â
</p>
<p>Any ideas?</p>
<p>Nicolas</p>
<p>QGIS 3.18.2 on Windows 10 </p>
<p>Â </p>
<p>Â </p>
<p>Â </p>
<pre>-- </pre>
<pre>Nicolas Cadieux</pre>
<pre><a href="https://gitlab.com/njacadieux" target="_blank">https://gitlab.com/njacadieux</a></pre>
</div>
</blockquote>
</div>
</div>
</div>
</div>
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</blockquote>
</div>
</blockquote>
<pre cols="72">--
Nicolas Cadieux
<a href="https://gitlab.com/njacadieux" target="_blank">https://gitlab.com/njacadieux</a></pre>
</div>
</blockquote></div>