Getting field value in Print composer label

Question

I am using QGIS print composer. I have so many images to export with a specific label. The text of the label is existing in a field of a layer.

I have tried to use this expression attribute( get_feature( 'Metro_Ring','S','1'),'Route') but the result is NULL.

where:

Metro_Ring --> name or ID of the table

'S' --> the field for selection.

1 --> the value that selects the row of interest.

'Route' --> the name of the field of interest.

I wonder if there is any error or a different method to get the value of the field 'Route' in the label.

Is field S numeric? In which case try referring to value 1 as numeric (1) - without using quotes as that might suggest it is a a string. Also, all layer and field references here are case sensitive so make sure they match. — she_weeds, Apr 13, 2020 at 21:51
Field S is numeric and I have written value 1 without quotes but I have got the same result. also, I have checked the layer and fields name and it does match.@she_weeds — Ahmed Alaa, Apr 14, 2020 at 5:08
OK, well I'm assuming you're using this expression in a text box in Print Composer? Perhaps we could narrow down the problem a bit. When you open the expression editor (by clicking Insert Expression), what does the Output preview show when you use just the get_feature('Metro_Ring','S',1) expression - does it return NULL or <feature : 0> (or some number other than 0)? If it's NULL then either the feature doesn't exist or you still have the layer/field reference wrong (maybe there is a trailing space in the layer name? Note this is the layer name in QGIS, not necessarily the filename) — she_weeds, Apr 14, 2020 at 5:16
It is my fault. I have tested the function on a feature with a NULL value in 'Route' field. But the main problem solved by removing the quotes from value 1 because field 'S' is a numeric field. many thanx for you.@she_weeds — Ahmed Alaa, Apr 14, 2020 at 5:32

Ahmed Alaa · Accepted Answer · 2020-05-03 20:11:45Z

1

S field is numeric so value 1 should be reffered as numeric (1).

The function would be as follow attribute( get_feature( 'Metro_Ring','S',1),'Route')

answered May 3, 2020 at 20:11

Ahmed Alaa

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