How to set widget type to 'Attachment'?

Question

I would like to make an open file dialog to appear in a field in the attribute table of a vector layer. I guess I need to set widget type to 'Attachment' for that field and to check 'Display button to open file dialog'.

I also guess I should use the QgsEditorWidgetSetup class, but I am not sure how to set the configuration options. I wrote something like:

setup=QgsEditorWidgetSetup('Attachment',{???}) #What should I write in {}?
layer.setEditorWidgetSetup(2,setup)

I have found examples for Date/Time and Value Map types, but what about Attachment?

Answer 1

Solving this particular question

The attachment widget is of type 'ExternalResource'. This is an example for you to configure it:

FIELD = "field_name"

editor_widget_setup = QgsEditorWidgetSetup(
    'ExternalResource', 
    {
        'FileWidget': True,
        'DocumentViewer': 0,
        'RelativeStorage': 0,
        'StorageMode': 0,
        'DocumentViewerHeight': 0,
        'FileWidgetButton': True,
        'DocumentViewerWidth': 0,
        'FileWidgetFilter': ''
    })
index = layer.fields().indexFromName(FIELD)
layer.setEditorWidgetSetup(index, editor_widget_setup)

---

More generic answer (recommendation)

As you can see, neither type nor config params for QgsEditorWidgetSetup are intuitive, and I guess you cannot find them currently in the docs. However, you could do some reverse-engineering:

1. Configure your field widget using the GUI.

2. Get the type and config for such widget:

   ews = layer.editorWidgetSetup(field_index)  
   print("Type:", ews.type())
   print("Config:", ews.config())
   

This way you can discover config keys and widget types.