[QGIS-Developer] array inconsistencies between QGIS and PostgreSQL

[Andreas Neumann]

Hi,

I have a PostgreSQL table with columns of type array (like int4[4] or 
text[]).

Now I have issues in QGIS when trying to save a QGIS array to this 
PostgreSQL array.

Arrays in QGIS use a square bracket notation, array in PostgreSQL use a 
curly braces notation.

Now if I try to save a QGIS array (result of an expression) to this 
PostgreSQL array column, it fails.

If I formulate the expression such, that the array starts/ends with 
curly braces, I can save the array in PostgreSQL, but it wouldn't load 
in the "list" widget, which is supposed to work with an array. The 
documentation claims "List: Displays a single column table to add 
different values within a single field. This is currently supported by 
the PostgreSQL provider, for fields of array type." (from 
https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/vector_properties.html#edit-widgets 
).

Does someone know how I can properly populate a "list widget" with an 
array, or at least make the array work properly with at "Text" widget? 
The latter would also be acceptable, but the list widget would be nicer.

Here is what I tried:

overlay_intersects(layer:='AV Gemeindegrenze', expression:=bfs_nr)
  --> returns, f.e. [2555,2554] as a QGIS array

and

'{' || array_to_string(overlay_intersects(layer:='AV Gemeindegrenze', 
expression:=bfs_nr)) || '}'
--> returns, f.e. {2555,2554} as a string

Neither way works properly. The latter way let's me at least save the 
data in PostgreSQL, but it wouldn't display correctly in QGIS (tried 
LIST and Text widget).

Thank you for your help!

Andreas
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