Expression parser: some expressions evaluate to NULL when they shouldn't

[qgib]

Author Name: Alister Hood (@AlisterH)
Original Redmine Issue: 4441

Redmine category:vectors
Assignee: Martin Dobias

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example 1:
I can create a string attribute field called "test1" and fill it using @$perimeter@
I can then fill it using @toint(test1)@
But the entire column is set to NULL if I try to do this in one step using @toint($perimeter)@

example 2:
With the new expression based labelling in Trunk, with some expressions the result displays OK in the "expression based label" window's preview, but no labels are drawn on the canvas. e.g. this expression: @toreal(toint($AREA/100))/100@

But for some reason I can build a larger expression which includes it, and the labels are drawn successfully:
CNAME || '
SMU '|| CNUMBER || '
AREA = ' || tostring(toreal(toint($AREA/100))/100) || ' ha'

[qgib]

Author Name: Nathan Woodrow (@NathanW2)

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I have just changed the title because it's related to the underlying expression parser more then anything else.

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• must_fix was changed from to Yes
• subject was changed from Labelling/Field calculator: some expressions evaluate to NULL when they shouldn't to Expression parser: some expressions evaluate to NULL when they shouldn't
• assigned_to_id was configured as Martin Dobias

[qgib]

Author Name: Martin Dobias (@wonder-sk)

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Fixed in 699694

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• resolution was changed from to fixed
• status_id was changed from Open to Closed

[qgib]

Author Name: Alister Hood (@AlisterH)

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I guess I should maybe open a new ticket - there is still be a problem for labelling.

As far as I can tell, the field calculator is working correctly, e.g. I can now fill a field with @toint($perimeter)@, or @regexp_replace( toint($area) ,'(\\d+)(\\d{3})','\\1,\\2')@, and I can label with fields created that way.

But if I try to use either of those expressions for labelling, the label is shown correctly in the output preview, but no labels are drawn on the map.

[qgib]

Author Name: Alister Hood (@AlisterH)

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Actually, it seems like the labelling doesn't work with any expression except a field name. e.g. no labels are shown if I use the expression @1@ or @1+1@ or @$perimeter@

[qgib]

Author Name: Nathan Woodrow (@NathanW2)

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I noticed this too. I think I know what might be causing the issue.

My guess is that how I'm using QgsExpression::evaluate() is wrong.

In the widget I use:

QVariant value = exp.evaluate( &feature, mLayer->pendingFields() );
</code>

but in the labeling class I use:

QVariant result = exp->evaluate( &f, layer->dataProvider()->fields() );
</code>

Will patch it and see if that makes any difference.

[qgib]

Author Name: Nathan Woodrow (@NathanW2)

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Opened a new ticket at #14418 and supplied a patch.