[Qgis-user] Problem using Model Inputs variable in an Select by expression in the model Designer

[Richard McDonnell]

Nicolas,
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 @NamelengthField != @NamelengthField || '2', should it not be more like your previous example Length != Length2

Regards,

Richard



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From: Qgis-user <qgis-user-bounces at lists.osgeo.org> On Behalf Of Nicolas Cadieux
Sent: 20 July 2021 09:27
To: Qgis Users List <qgis-user at lists.osgeo.org>
Subject: Re: [Qgis-user] Problem using Model Inputs variable in an Select by expression in the model Designer

Hi,
Does anyone have an idea?
Nicolas Cadieux
https://gitlab.com/njacadieux


Le 8 juill. 2021 à 01:17, Nicolas Cadieux <njacadieux.gitlab at gmail.com<mailto:njacadieux.gitlab at gmail.com>> a écrit :


Hi,

I am creating a model that fixes Network files before they are used in the QGIS Network analysis (Shortest path) tools.

This is my work flow:

  1.  Create a "Length" field (value) and calculate $length in the field calculator
  2.  Split the Multipart lines into Singlepart lines
  3.  Create a "Length2" field (value) and calculate $length in the field calculator
  4.  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)

This works well

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:

  1.  User input "Length" in the Model input. (@NamelengthField)
  2.  Create a "Length" field using  @NamelengthField (as pre-calculated value) and calculate $length in the field calculator: This is OK
  3.  Split the Multipart lines into Singlepart lines: This is OK
  4.  Create a "Length2" field using  @NamelengthField ||'2'  (as pre-calculated value) and calculate $length in the field calculator: This is OK this field (Length2) is created and calculated properly.
  5.  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.

I tried stuff like

@NamelengthField != (@NamelengthField || '2')

'@NamelengthField != @NamelengthField || '2''

"@NamelengthField != @NamelengthField || '2'"

"@NamelengthField"|| !=|| "@NamelengthField || '2'"

Even simple @NamelengthField = 5.286365157529550 (which should extract exactly one value).

Any ideas?

Nicolas

QGIS 3.18.2 on Windows 10







--

Nicolas Cadieux

https://gitlab.com/njacadieux
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