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I am currently using data defined properties and labeling to present pipes based on diameter. I now have a dictionary table that has id's for every combination of diameter and material and I'm using it with the value relation widget.

I must find a way to access the value represented by the key in the diameter || material field.

An ugly way that solves this would be to use:

CASE
   WHEN id_material_diam in (id1, id2) THEN result_formula_containing_diameter
   WHEN id_material_diam diameter in (id3...) THEN ...
END

Is there an elegant way that I can access the actual values for which the ID is the key?

I am using QGIS 2.2 Valmiera

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  • Have you tried to create a new column out of the two using the field calculator? – AndreJ Mar 13 '14 at 7:21
  • Instead of diameter + material (e.g. 300 Stell) I have now an id. The value behind the id shows on account of the value relation widget. The question is how to have this in the expressions. I know how to create a new column and fill it with the actual values but that would be redundant and I want to avoid that. Thank you anyway – tudorbarascu Mar 13 '14 at 7:42
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    Have you tried to create a join to the other layer? – Matthias Kuhn Mar 13 '14 at 8:34
  • Although not what I expected, that's clearly a more elegant solution. I guess sometimes one must be told that 1 + 1 = 2 Thank you Matthias. – tudorbarascu Mar 13 '14 at 10:47
  • Unfortunately I encountered a bug: hub.qgis.org/issues/9783 as I wanted to use the values in data defined properties. – tudorbarascu Mar 14 '14 at 7:23
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Matthias Kuhn has an acceptable answer although it's in the comment. Joining the dictionary table by ID and maybe hide the unneeded columns is enough.

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