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I have expressions for a table field that has a map layer named as a data source file (building_ex.shp). I plan to save this setting as a style and use it in other projects, but in other projects the layer with this data source file can be named differently (BUILDINGS; real estate; facilities).

Is it possible to make this expression more universal, so as not to change it in each project?

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    Did you consider "project variables"? You can access them by using @project_variable - perhaps there is a hidden solution?
    – MartinMap
    Commented Mar 9, 2023 at 8:59

1 Answer 1

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You could do something like this. Admittedly, the expression can probably be cleaned up.

with_variable('existing_layer_name',
    with_variable('options', array('buildings', 'facilities', 'real estate'),  -- pre-determined list of layer names 
        with_variable('layer_names', array_foreach(@layers, layer_property(@element, 'name')),

            array_get(@options,
                array_filter(
                    array_foreach(
                        @layer_names,
                        array_find(@options, @element)
                    ),                      
                    @element > 0
                )[0]
            )
        )
    ),

    -- the original expression
    aggregate(
        layer:=@existing_layer_name,    -- the result of the matching procedure above
        aggregate:='sum',
        expression:="value"
    )
)

It basically matches the layer names in the project against a pre-determined list. If more than one match is found then it uses the first one.

array_find returns the index of the found element, and array_get uses that index to pull the layer name from the array of 'options'. array_filter is used to remove any -1 returned by array_find (non-matching).

The following two screenshots omit the original expression to demonstrate what is returned by the match.

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enter image description here

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