skip_row does not detect the difference when m2m objects are being updated

skip_row method does not the difference between ManyToMany objects in instance or original because the instance related objects remain unchanged.

When using skip_row all models where m2m changed are detected as unchanged thus the whole transaction is skipped

[mxreppy]

Am I missing something or did you cache the file row data in _row somewhere else (looking at the 0.7.0 & 1.0.0 releases

[raphodn]

I also struggled to update a M2M field which was defined like this:

tags = fields.Field(column_name="tags", attribute="tags", widget=ManyToManyWidget(Tag, field="name"))

What I ended up doing was to write custom code in the import_obj() method, where I manually compare the instance.tags with the row.tags, and do a instance.tags.set() with the corresponding ids (having transformed the tag names into ids beforehand). More importantly, and similarly to a comment above, I add self._m2m_updated = True (False if no changes) before calling super, so that I’m able to set skip_row() to False for these rows.

Please let me know if there is something easier to do 🤔 🙏

Full code below, hope it helps 😃

class QuestionResource(resources.ModelResource):
    category = fields.Field(
        column_name="category",
        attribute="category",
        widget=ForeignKeyWidget(Category, field="name"),
    )
    tags = fields.Field(
        column_name="tags", attribute="tags", widget=ManyToManyWidget(Tag, field="name")
    )

    def import_obj(self, instance, row, dry_run):
        """
        Manually manage M2M column
        - tags: get the row's comma-seperated tags, query their corresponding ids, check if they are
        different than the instance, and finally set them to the instance
        """
        self._m2m_updated = True
        if instance.id:
            tags = row.get("tags")
            tag_ids = []
            if tags != "":
                tags_split = tags.split(",")
                # Tag.objects.filter(name__in=tags_split) # ignores new tags
                for tag_string in tags_split:
                    # tag, created = Tag.objects.get_or_create(name=tag_string)
                    tag = Tag.objects.get(name=tag_string.strip())
                    tag_ids.append(tag.id)
                tag_ids.sort()
            if list(instance.tags.values_list("id", flat=True)) != tag_ids:
                instance.tags.set(tag_ids)
                self._m2m_updated = True
        super(QuestionResource, self).import_obj(instance, row, dry_run)

    def skip_row(self, instance, original):
        """
        Highlight row if M2M column was updated
        """
        if self._m2m_updated:
            return False
        return super(QuestionResource, self).skip_row(instance, original)

    class Meta:
        model = Question
        skip_unchanged = True
        report_skipped = True