add AttachmentsMixin

attachments/mixins.py

@@ -0,0 +1,102 @@
+from django.core.exceptions import ImproperlyConfigured
+
+
+class AttachmentsMixin:
+    """
+    This mixin is intended to be used with a form so that attachments functionality
+    can be tied in with the form itself. It handles all of the attaching and deleting.
+
+    To use this mixin, first create a class that inherits from it so that the
+    ``get_session_error_message`` can be overridden.
+    Then, make it a superclass of an existing ``ModelForm``.
+
+    Due to method resolution order, make this mixin the left-most superclass.
+    For example, ``class MyForm(MyAttachmentsMixin, forms.ModelForm)``.
+
+    The ``__init__`` method does the following:
+        - Make ``session`` and ``attachments_field_name`` instance variables.
+        - Keep track of files that will be deleted.
+
+    :param session: an already-created session
+    :type session: optional
+    :param attachments_field_name: the name of the field on the model that represents the attachments
+    :type attachments_field_name: str, optional
+    """
+    def __init__(self, *args, session=None, attachments_field_name='attachments', **kwargs):
+        self.session = session
+        self.attachments_field_name = attachments_field_name
+        self.attached_files = []
+        self.session_error = None
+        # This needs to be done since args may be (), (None, ), or (x, ...) where x is truthy.
+        if args and args[0] and args[0].get('delete-attachments'):
+            try:
+                # If this is QueryDict, must use getlist.
+                self.deletions = [int(pk) for pk in args[0].getlist('delete-attachments')]
+            except AttributeError:
+                # If this is any other mapping, must use get.
+                self.deletions = args[0].get('delete-attachments')
+        else:
+            self.deletions = []
+        super().__init__(*args, **kwargs)
+
+    def is_valid(self):
+        """
+        :returns: ``True`` if both the form and session are valid.
+        """
+        return all([super().is_valid(), self._session_is_valid()])
+
+    def _session_is_valid(self):
+        """
+        :returns: ``True`` if the session is valid.
+        """
+        if not self.session:
+            return True
+        self._clean_session()
+        return not self.session_error
+
+    def _clean_session(self):
+        """Add a session error, if necessary."""
+        if not self.session.is_valid():
+            self.session_error = self.get_session_error_message()
+        return self.session_error
+
+    def get_session_error_message(self):
+        """
+        :returns: a string containing the session error message
+        """
+        raise ImproperlyConfigured('Please implement this method so that a session error message will display.')
+
+    def uploads_exist(self):
+        """
+        :returns: ``True`` if uploads exist.
+        """
+        return bool(self.session) and self.session.uploads.exists()
+
+    def has_changed(self):
+        """
+        :returns: ``True`` if the form or session has changed.
+        """
+        return super().has_changed() or bool(self.deletions) or self.uploads_exist()
+
+    def save(self, commit=True):
+        """
+        Attach uploads from the attachment session to the ``ModelForm`` instance, delete the session,
+        and perform any deletions specified by the POST data.
+        """
+        instance = super().save(commit=False)
+
+        base_save_m2m = self.save_m2m
+        def save_m2m():
+            base_save_m2m()
+            if self.uploads_exist():
+                self.attached_files = self.session.attach(instance)
+                self.session.delete()
+
+            getattr(instance, self.attachments_field_name).filter(pk__in=self.deletions).delete()
+        self.save_m2m = save_m2m
+
+        if commit:
+            instance.save()
+            self.save_m2m()
+
+        return instance