Add basic "downloadable" support for ExportMasterView

instead of it trying to do its own thing for that...  more to come on this

tailbone/views/exports.py

@@ -45,7 +45,10 @@ class ExportMasterView(MasterView):
     """
     creatable = False
     editable = False
+
+    # TODO: should deprecate `export_has_file` in favor of `downloadable`
     export_has_file = False
+    downloadable = False
 
     grid_columns = [
         'id',
@@ -126,6 +129,8 @@ class ExportMasterView(MasterView):
             f.set_readonly('record_count')
 
         # download
+        # TODO: should probably stop doing this altogether?  and just make each
+        # derived view declare the field renderer?
         if self.export_has_file and self.viewing:
             # download = forms.renderers.FileFieldRenderer.new(
             #     self, storage_path=self.rattail_config.export_filedir(self.export_key),
@@ -202,6 +207,7 @@ class ExportMasterView(MasterView):
         model_title = cls.get_model_title()
 
         # download export file
+        # TODO: should deprecate this and just use 'downloadable' instead
         if cls.export_has_file:
             config.add_route('{}.download'.format(route_prefix), '{}/{{{}}}/download'.format(url_prefix, model_key))
             config.add_view(cls, attr='download', route_name='{}.download'.format(route_prefix),

tailbone/views/master.py

@@ -2767,6 +2767,13 @@ class MasterView(View):
         """
         return getattr(cls, 'mobile_row_form_factory', forms.Form)
 
+    def download_path(self, obj, filename):
+        """
+        Should return absolute path on disk, for the given object and filename.
+        Result will be used to return a file response to client.
+        """
+        raise NotImplementedError
+
     def render_downloadable_file(self, obj, field):
         filename = getattr(obj, field)
         if not filename: