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

[Charles Dixon-Paver]

Hi Nicholas,

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:

with_variable('Length2',  to_string(@NamelengthField) || '2',
if(attribute(to_string(@NamelengthField)) != attribute(@Length2), TRUE,
FALSE))

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.

Regards

On Tue, 20 Jul 2021 at 10:46, Richard McDonnell <richard.mcdonnell at opw.ie>
wrote:

> 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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> *FRM Data Management*
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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> 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 "Length*2*" 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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