Refactor to use same sorting method as other models

Other models sort based on their `__sort_attribute__`. This commit moves
the calculation of each files position in the template into the
`TemplateEmailFile` object, so that its sorting can also work in this
way.

Author: quis

app/models/template_email_file.py

@@ -28,7 +28,7 @@ class TemplateEmailFile(JSONModel):
     validate_users_email: bool
     pending: bool
 
-    __sort_attribute__ = "filename"
+    __sort_attribute__ = "position_in_template"
 
     @staticmethod
     def create(*, filename, file_contents, template_id, pending=True):
@@ -110,6 +110,10 @@ def file_contents(self):
             f"{self.service_id}/{self.id}",
         )
 
+    @property
+    def position_in_template(self):
+        return self.template.index_of_placeholder(self.filename)
+
 
 class TemplateEmailFiles(SerialisedModelCollection):
     model = TemplateEmailFile
@@ -123,9 +127,6 @@ def __init__(self, template):
         email_files = template._template.get("email_files", [])
         super().__init__(email_files)
 
-        position_in_template = (template.index_of_placeholder(email_file.filename) for email_file in self)
-        self.items = sorted(email_files, key=lambda _: next(position_in_template))
-
     def __getitem__(self, index):
         return self.model(self.items[index] | {"service_id": self.service_id, "template": self.template})
 

app/templates/views/templates/email-template-files/files-list.html

@@ -20,7 +20,7 @@
 
    {% set files = [] %}
     {%  if template.email_files %}
-    {% for item in template.email_files %}
+    {% for item in template.email_files | sort %}
       {% do files.append(
         {
           "key": {